David Wall, a Sea King pilot from the mid-1960's era, indicates the Sea king was only fitted with the following  electronics:  UHF radio, one HF radio, IFF, ADF, Tacan, Doppler and a Radio Altimeter plus a Dipping Sonar.

Ian Snow who did three tours as a TACCO (Air Navigator) on the Sea King offers some insight into the Sea King's electronics suite during the time he served.

"I first went to the Sea King in the Spring of 1973 joining HS-50 Squadron which split into HS 423 and HS 443 Squadrons about 18 months later.  From 1976-79 I served in  443 Squadron and again in 1985-86. For communications, the helicopter was fitted with the AN/ARC-552 UHF set, the ARC-505 (Collins 618T) HF transceiver and the Collins CU-351 Antenna tuner.  The HF antenna was the standard USN Sea King fit. It came out of the hull on the port side just aft and above the passenger window, went forward to a short mast on top of the port sponson, then back to the tail boom.  The Shearwater Base frequency was something like 5718 KHz but the antenna wasn't very efficient at that frequency.

On the 20 metre amateur band it did however work well.  Amateur radio operator Brit Fader VE1FQ [1] ,  used to do the odd phone patch for me if we were far enough from the ships.  We were almost always under imposed HF radio silence.  The call sign exchange was "Brit are you there?"  followed by a "Standby" and a phone ringing.


The upper limit was 20 MHz for the Sea King using the CU-351 antenna tuner.


The Sea King didn't receive aeronautical VHF until 443 Sqn went to Patricia Bay in British Columbia. Since this was a civilian airfield, it didn't have military UHF (225 to 399 MHz) capability.

As part of the CH-124A upgrade circa mid-70's, the Sea Kings were fitted with a Wolfsburg commercial VHF FM set.  The radio box was the same but that there were several control heads that could be used depending on the role.  We had an 8-channel model but you had to pull the control head out of the console in order to program the thing.  The reason we had it was for marine SAR, usually monitoring channel 16.

We had the trusty AN/ARC-552 when I first went onto the Sea King.  They upgraded it but I don't recall what the new model was.  They also upgraded the TACAN.   There was an electronics compartment under the pilot's feet and slightly forward.  Access was through a huge door that formed the bow.  All that the  tube gear was replaced by radio equipment that went into the floor console between the pilots.  Eventually "lead pigs" had to be installed up front to keep the center-of gravity  in bounds.

The Nestor Secure Voice system was a total disaster.  We discovered after awhile that the problem was mostly with the narrow bandwidth of the ARC-552 radio. Basically if you couldn't see the other aircraft you couldn't talk to it.  The upgrade to Vinson Secure Voice and the upgrade to modern radios eventually fixed the situation.

In order to locate submarines, the Sea King's latest sonar uses a transducer ball at the end of a 450 foot cable. It can also be fitted with FLIR (Forward Looking Infra-Red) to find surface vessels in the dark of night".

The electronics suite in the table below was derived from two main sources:
1) RCN Aircraft General Information Data , May 1,1963.
2) An extract showing antenna placement circa mid 1980's.

The list is incomplete since the current electronics suite (2010) is not known and due to the long service life of the Sea King, it is nearly impossible to track every equipment revision. If anyone can help refine this list, contact:

1963 original fit  AN/AQS-10  Airborne, active-only, dipping Sonar manufactured by Bendix. Range of 2 nm.  Suspended from a 250 foot cable. 
1972 conversion 
to model 'A'
AN/AQS-502 The CH-124A uses the Bendix AN/AQS-502 dipping sonar, a Canadian version of the AN/AQS-13B . It uses a transducer ball on a 443 foot (135 metre) long cable and usually deployed from an altitude of 60 feet above the sea. Range is 1 nm.  (Need photo). 
1963 original fit  AN/APN-130  The AN/APN-130 is a CW Doppler navigation set designed primarily as an all weather ground velocity indicator for helicopters, airships, and other aircraft with hovering or negative speed characteristics. 
By mid 1980s  AN/APN-503(V) Doppler radar made by Canadian Marconi. Provides ground speed and track between altitudes of  0 to 50,000 feet. Used by the pilot and co-pilot. (Need photo) 
1972 conversion to model 'A' AN/APS-503 I-band surface Search radar. Range of 70 miles max. Manufactured by Litton Systems Canada. It was very basic in capability with none of the Fast or Slow Time Constant characteristics  found on a real anti-submarine radar.  Litton used the helicopter's 400 Hz A.C. power system as the PRF (Pulse Repetition Frequency) generator, which meant anybody with a basic ESM system could figure out exactly what was happening as the main rotor speed changed with power settings and bearing would stay constant while in the dip. The antenna is behind the main transmission so there's a +/-15 degree or so blind sector directly ahead of the helicopter.  (Need photo)
1963 original fit  AN/ARN-501 TACAN ARN= Airborne, Radio, Navigation 
By mid 1980s  AN/ARN-504 TACAN .ARN= Airborne, Radio, Navigation. (Need photos and info)
Mid 1960s?  AN/ASN-501 Tactial Plotter. (Airborne, Special Type, Navigation)
Late 1990's AN/ASN-123 Tactical Doppler/Inertial Navigation Set. By the late 1990's and in order to improve mission performance, Canada acquired some USN surplus AN/AS-123 Tactical Navigation Systems in order to replace the antiquated AN/ASN-501 Tacan that were installed in twenty three of the Sea Kings. (ie the twenty two CH124A's and the one "Waterbird"). The six CH124B's plus the HOTEF bird were already converted by the Spring of 1998. This system has been de-installed from all aircraft as of June 2015. 
1963 original fit  AN/APX-25  L-band IFF transponder. Range: 800-1300 MHz, output 1 KW pulsed. 

SIF panel (Courtesy Old Cockpit Panels)

By mid 1980s  AN/APX-77A IFF (need photo and specs)
By mid 1980s AN/ARR-52A Sonobuoy receiver. (Need photo and specs)
? OTPI The acronym  means On Top Position Indicator. It is a VHF receiver system capable of providing relative bearing information from the helicopter  to any of the 31 different sonobuoy channels. 
By 1998 AN/UYS-503 Sonobuoy Processing System. This is a digital processor built by Computing Devices Company for the processing of signals received from up to eight standard sonobuoys or a dunking sonar.
1963 original fit  AN/ARC-94 
Collins 618T-1
Airborne H.F. Radio  2-29.999 MHz, 1 kHz channel spacing; Modes: USB, LSB, AM and FSK; 400 watts PEP on SSB. Major components: RT-698 receiver/transmitter and C3940 Control box. . Power requirements: 208VAC 400 Hz; Weight 59 lbs. Includes R-T, control and mounting.  The ARC-94 is the military version of the Collins 618-T1.  Made by  Rockwell-Collins. 
618T photo (by John Mackesy VK3XAO)
By mid 1985 AN/ARC-505(V) H.F. Radio This was the military version and Canadian version of the Collins 618T radio.
618T photo (by John Mackesy VK3XAO)
Likely fitted as original equipment in 1963. CU-351/AR HF antenna tuner made by Collins Radio. It provides automatic tuning of fixed aircraft antennas and efficient transfer of RF power from the 52 ohm output of a 50-150 watt transmitter into such antennas. It consists of two motor driven ceramic rollers and a variable capacitor in a sealed glass envelop similar to an EIMAC tube, with pins on the bottom to fit into a socket.  A long, flat  silver plated wire was reeled between the rollers to change the inductance. Circa 1956. 

Unit photo (by John Mackesy VK3XAO)

All "B' variants retrofitted  AN/ARC-210 Unit info courtesy Rockwell-Collins.  Radio system. 30 to 512 MHz frequency range. It
1963 original fit  AN/ARC-552 U.H.F Receiver/Transmitter; 225 to 400 MHz with independent Guard receiver for 243 MHz.  Power output: 20 watts average. 
Unit photo  (Photo courtesy Canadian Navy) 
During 'A' refit of 1972 ? Wolfsberg FM radio. 
By mid 1980s  AN/ARC-552B U.H.F. Radio
By mid 1980s  AN/ARC-511 V.H.F. AM Radio (Need photo)
By mid 1980s  AN/ARC-513 V.H.F FM Radio (Need photo)
1963 original fit  AN/AIC-14 Interphone. Pictured is the C-12595 control panel. (Photo courtesy E-bay)
1963 original fit. Still fitted in mid 1980's and appears in a 2009 photo. AN/ARA-25A UHF ADF 
1963 original fit  AN/APN-117  Low-Level Radar Altimeter, 0 to 1,000 feet. Used in combination with AN/APN-22; Manufactured by Electronic Assistance Corp
By mid 1980s  AN/APN-171(V)3  Height Finding radar.
By mid 1980s  AN/ARN-59  L.F. Direction Finder
1963 original fit  AN/ASA-13A Navigation computer. Manufactured by Loral. Circa 1960.
Late 1970's KY-28 Nestor family voice encryption. The control box  was on the TACCO's console
By 1985/86 ? Vinson voice encryption system with the electronic FILL keying system. 
1963 original fit  DCU -77A  Armament Control Monitor
1963 original fit  MA-1  Magnetic Compass System. It is slaved and directional gyro stabilized. (4 degrees per hour).
1963 original fit  ID-864A  Hover Indication System 
By mid 1985 CPI (Crash Position  Indicator equipment)
  seaking_ch124a_tactical_ panel_s.jpg Sea King Tactical panel circa 2000.  Click to enlarge. (Image by Ross Spenard)
  FLIR-2000 Infrared camera. Now de-installed from all aircraft as of June 22/15

The AN/AQS-10 sonar was an original fitting on the Sea King in 1963. (From the collection of David Wall). 

seaking_sonar_deployed_s.jpg Mid 1960s: This Sea King is flying over land with its AN/AQS-10 sonar transducer deployed. Click to enlarge. (From the collection of David Wall). 

The dome was supposed to hit the water just as the helicopter's ground speed hit zero. It had to be down about 50 feet or so before the cable became stable.

December 7, 2009 in the Gulf of Aden: Corporal Kevin Ferguson, an AVS Tech aboard HMCS Fredericton with the Air Det crew, does a weekly inspection and maintenance of the Sea King helicopter. Here he is inspecting the electronics bay which is located under the pilot's compartment. A waterproof access door, shaped like the bow of a boat, closes up the compartment. 

In the lower left corner is the Collins 618T radio. The grey box to its right is believed to be a
TACAN made by  Canadian Marconi. The ARA-25 UHF ADF is in the vicinity of the technician's left hand.   (Canadian Forces  photo # HS2009-N046-003 by Corporal Peter Reed)

ea king ae_layout_mid1980s_s.jpg This diagram shows the placement of the Sea King's antennas circa January 1985. Info from this diagram was used to derive much of the mid 80's electronics suite.  (From the Sea King Handbook provided by Ian Snow) 
The Sea King had two UHF antennas, one on the upper side above the tail wheel (referred to in the manuals as the Alternate) and the other under the boat hull.  The pilots had an antenna switch somewhere in the front office.  In practice, the switch was always in the Alternate position on the theory that the above-water antenna would be more useful after a ditching.   In the original Sea King, the two antennas were identical.  In the modified CH-124A version, the antenna was replaced with a dual UHF/VHF antenna which was distinctly different. Mounted aft  and midway-bottom on the boom, it was capable of bending 90 degrees under the helicopter so it wouldn't get damaged during landings.

In the Sea King, in order to dip the sonar dome, the pilot would establish forward flight at 150 feet altitude and 100 kts into the wind based on the barometric altimeter and on the TACCO's "mark dip" command would punch the "coupler" button.  The coupler would then bring the helicopter down to a hover at 40 feet ASL based on the radar altimeter reading.  As the Doppler radar was transitioning from forward flight mode into hover mode (+/- about 10 kts) the pilot would order the sonar dome down and the ball would go into the water at about the time zero speed was reached . Zero was relative to the earth's surface since the helicopter is really flying forward at the speed of the wind. The Doppler radar is manually compensated for the direction and speed of the moving sea - swell and/or waves, none of which are necessarily going in the same direction let alone the wind.

Once the ball reached 50 feet (depth) the coupler would switch from using the Doppler radar as the reference to two angle sensors incorporated in the reeling machine and the coupler would 'fly' the helicopter  to maintain position vertically over the sonar cable.  In theory, if the radar altimeter failed the coupler would cause the helicopter to climb back up to 150 feet.

One of the Sea King's modifications was triggered by a failure of the radar altimeter while dipping the sonar transducer.  The problem was that it didn't quite fail (in which case the flight stabilization system would revert to the higher barometric altimeter setting); rather, it started to send bogus data which resulted in the hover control system lowering the helicopter rather than raising it above water.  The radar altimeter emitted a CW transmission that swept from 4200 to 4400 MHz.  There was a coax timing delay line between the transmitter and receiver.  The calculated difference between the outgoing and incoming frequencies translated into distance above ground or sea surface.  There were three or four instances of the helicopter very gradually descending (with the first instance at night) over a pretty calm sea in fine weather.  On the first instance, the co-pilot leaned over and turned on the windshield wiper to clear "rain" from the windscreen.  A moment later the pilot, realizing that it was spray generated by the rotor wash, executed an "Emergency Streamer" - a controlled climb of several hundred feet until the sonar ball broke the water, followed by a transition into forward flight and recovery of the sonar cable/dome.  On the second occurrence of the problem, the waves were touching the tail wheel causing the helicopter to pitch.  That was followed by a couple of daytime instances when the crew was able to maintain a manual (visual) dip and assess what was really going on.  The situation resulted in an operational restriction on night dipping that lasted for 3 years until a fix was developed for the radio altimeter.

A temporary fix to the problem was to equip the helicopters with active sonobuoys and sonobuoy receivers taken from the retired Argus a/s aircraft.  This system was not supplied with chart recorders, just chronometers to measure the time between the active "ping" and the received echo.  It was very elementary indeed. The ideal system would have been a proper passive acoustic system like the ASQ-13C dipping sonar which had a passive acoustic processor incorporated in it.


Getting radar into the Sea King revolutionized operations. Until then, the ship had radar-controlled the helicopter  much as if they were on the end of a string. Although the APS-501 was not the best antisubmarine radar, it could at least find Mother (the ship) who refused to turn on Father (the TACAN). It allowed the crew to do their own radar, self-controlled landing approach.  Because of the radar blind spot produced by the rotor transmission, the pilot would bring the ship down the upwind side of the blind arc and a good TACCO (Tactical Coordinator, code word PLAYBOY) could bring the pilots into a 175-200 yard proximity of the ship's hangar.  It took lots of practice but the technique prevented  a ditching at sea on a foggy night.


The outputs from the navigation equipment would be fed to some form of amplifier which would send the information to the display instrument.  Some aircraft would have only magnetic orientated instruments, other (naval/maritime) aircraft would have a true north display capability.

For example, in the Sea King the BDHI (Bearing Distance Heading Indicator) had a rotating compass card that could be selected to True North, Magnetic North or Track.  In tactical mode, the pilots would select Track since  the TACCO was giving them a true bearing (#1 needle) and distance to go to the "Mark Gate" point for the next dip.  The pilot was actually flying some variant of an 'S' type pattern since he had to go into and out of the dip heading into wind (the sub of course would try to escape down-wind to minimize the amount of time that contact  could be maintained.  When flying an approach to an airport the pilots would select "Mag" since all civil air operations use magnetic headings.

Speaking of navigation, there is an old tale where the controller orders a 1° turn to the right. When the pilot replies that nobody can fly that accurately, the controller says “OK turn left 9°”  followed by “Turn right 10°”.


David Wall, a former Sea King pilot, provides some background on the ASN-501. "It was a tactical navigation plotter and was first installed in the Tracker. When I was at Shearwater, it was still at VX-10 Squadron with the first units just making their way into the aircraft at VS-880. Prior to that, the navigation and plotting of sonobuoys was done by the co-pilot using a Mk VI plotboard on his knees, his control column having been stowed away out of sight.

The ASN-501 was a great improvement over the "board". It had a mechanically driven plotting screen about a foot square and centrally mounted between the pilots on the front instrument panel. It was very crude by modern digital standards but a great advance in those days. I left Shearwater in 1966 and sometime fairly soon thereafter, the 501 found its way into the Sea King but for a variety of reasons it was placed in the back and operated by the crew stationed there. I think there were several reasons for this decision – lack of space up front, a requirement for both pilots in the Sea King to be in the “flying loop” especially low level at night, availability of a crew in the back The only sensor back there at that time was the sonar and that just took one man to operate. Probably the real reason was that integration/unification of the Canadian Forces was underway with the Airforce taking over what had been naval aviation, and the Airforce had tons of navigators looking for work.

None of the above is to be confused with TACAN, which is simply a navigation system that feeds bearing and distance information to round dial readouts on the instrument panel for the pilots. It was a naval system developed by the USN in the ‘50s and was a UHF equivalent to the civilian VHF VOR navigation system with the added feature of DME displaying distance (that VOR could not). In the ‘60s, most airways were VOR based and the TACAN stations were strictly military which made for some interesting cross-country flying since our RCN aircraft were TACAN (and ADF) only. Gradually, the civies realized the value of the DME readout so TACAN beacons were co-located with the VOR stations creating the now familiar VORTAC designator. TACAN frequencies were hidden to the pilot, who just dialed in a channel number,  whereas the VOR stations were selected by the frequency – eg. YOW 114.6 paired with Channel 93. Civilian aircraft simply added DME receivers which paired up with the appropriate frequency when a VOR station was selected".


The Teledyne Systems AS/ASN-123 was initially developed for the US SH-2F helicopters and then adopted for service in the SH-3H Sea King and the EA-6B Prowler. The set is a Tactical Navigation System but in helicopters it also provides the torpedo attack solution. In a helicopter, the main system display is in the cockpit but the TACCO has and operates the main system control panel.

The six Sea Kings (five deployed,  one reserve) converted to the anti-surface role for Gulf War 1 received the ASN-123 as part of the conversion.  The remaining helos would have been converted sometime later when the life extension program was commenced.


This is a Mk 6 plot board in use. The top opens to flip the large disk with the grid to change scales.  At the bottom was a pull-out rotary calculator for heading/track/drift/airspeed/ground speed calculations. It was in a very inconvenient location.  (Extract from a David Wall photo)

seaking_mk6_plotboard _02.jpg
Mk VI plotboard with circular calculator in the extended position. This artifact is on display in the Shearwater Aviation Museum.  (Photo by Ian Snow) 
seaking_mk6_plotboard _01.jpg
Close up of the pullout rotary calculator, part of the MkVI. (Photo by Ian Snow) 

This is a Mk VII Plotboard, somewhat similar to the Mk VI. It had extra features which the Mk VI didn't have. (Photo via E-bay)
Ian Snow explains the use of the Mk VI plotboard. "On the order of 14 inches square, it laid flat on the copilot's/TACCO's knees while plotting.  The jump distances where calculated using standard diameter turns and straight line runs were done on the basis of timing with a stopwatch.  Like the ASN-501, you kept a track plot in one (navigational) scale (the plane function in the ASN-501) and calculated the jump using a tactical scale.  The trick was to put a smoke/flame marker or Mod-9 sonobuoy (equipped with a light and dye marker) in the water to use as a reference point.  You could keep up with a 3 or 4 knot target but with a 12 knot O-Boat forget it."


This Calypso example survives at the Shearwater Aviation Museum. It was designed and built by Computing Devices Canada.  (Photo by Ian Snow) 
Calypso was an advanced acoustic processor (passive and active) in the HOTEF (Helicopter Operational Test and Evaluation Flight) lab at Shearwater, NS . It was being evaluated  as a candidate for a Sea King upgrade in support of the CANTASS tactical towed-array on Halifax class frigates. The flying version went down with the HOTEF Sea King when it suffered  a main transmission oil leak, ditched, and eventually sank.  It was flying from HMCS Fraser, the CANTASS towed-array trials ship.


Major Dwight Bazinet, known in Shearwater as "Baz",  comments on the Sea King's electronics fit to the extent that he can.  He is currently on his fifth posting to HOTEF and as of June 2015, is the Augmented Surface Plot (ASP) functional tech lead and lead software developer. For the Sea King, he indicates:

- the FLIR-2000 has been retired
- the ASN-123 has just been completely removed.
- the basic ASP is fitted in the TACCO position of all the aircraft. ASP is a system that optimizes the tactical plot
  by overlaying maps, radar, AIS, and tactical graphics. A detained article on ASP from Canadian Naval Review 
  Vol 9, No 1 (2013) can be viewed here.
- All Sea King  B models have ARC-210 radios.
- Installed is TCDL (Tactical Common DataLink). It is a mission kit which employs a high bandwidth radio that can move various information, including plot and video, to and from the ship; the actual box is a L-3 Comms Systems West CMDL).

The main thing we are doing with the Sea King now is using it to learn how to use the CH-148 Cyclone.

[1] Brit Fader VE1FQ, was dedicated amateur operator based in Halifax  who set up an innumerable amount of phone patches for military personnel. He was the first recipient of the Radio Amateur of the Year award when it was established in 1976 by the Canadian Radio Relay League.

Credits and References:

1) Ian Snow <va3qt-4(at)>
2) Leo Pettipas <lpettip(at)>
3) ARC-94 and ARC-102
4) David Wall <walld(at)>
4) AQS-502 reference
5) "CH-124A Sea King Helicopter HANDBOOK" dated January 1985 and issued by HT 406 Squadron (the Sea King OTU).
6) Canadian Defence Quartely. Spring 1998. Evergreen Sea King by Sharon Hobson.
7) ASN-123. The Naval Institute Guide to World Naval Weapons Systems 1997-1998 by Norman Friedman.
8) Major Dwight Bazinet  <bazasp(at)>

Back to Sea King Main Document
June 22/15