[HMCS Algonquin was fitted with the 276 radar set. This story, based on extracts from Radar at Sea by Derek Howse, shows how the set was developed and how it came to be the interim set until the newer 293 radar came into service.]

DEVELOPMENT

Once the program to test the "strapped" magnetron in the 271/3 'Q' series radar was under way in 1943, senior officers at the Admiralty Signal Establishment (ASE) started to plan for the next generation of centimetric radars in order to take advantage of the many technical developments which had occurred since the production of the 271 set.

The submarine threat had been contained, at least for the time being, but the threat from the air had intensified and ships were particularly vulnerable to attacks by low flying aircraft against which existing radar was not effective. Fighter direction techniques were being developed and there was a great need for better radar, not just for early air warning, but also to assist in fighter interception of enemy aircraft when between 15 and 70 miles away, the so-called Fighter Interception Zone. Better methods of height finding  were urgently needed.  By October 1942, the main features of the new designs had been settled and a detailed description was circulated to British naval staff in a document.

PERFORMANCE INTENTIONS

In the introductory paragraphs of the document, Mark III refers to the original series of radars, Mark IV to the improved 'Q' series and Mark V to the proposed new series, soon to be announced as types 276/277.

RDF (Radar Direction Finding) Type 276/277 Mark V is being developed to replace 271/273 Mark IV and 272/272P Mark III. The chief features of the new set will be:

a) Considerably increased power, even compared to Mark IV.
b) A single mirror, single parabolic aerial (type AUK) for 277 or
   sandwich type, mirror antenna type AUJ (single cheese) aerial for type
   276 with common transmitting and receiving arrangements. The aerial
   system will be exposed. There will be no 'lighthouse' structure.
c) PPI presentation.
d) Stabilization in azimuth.
e) In the case of Type 273 Mark V [ie the 277 set], stabilization in elevation also.
f) Larger radar office and in general, heavier equipment.

Although the production and fitting of Mark V sets was still some way off,  the Mark V development was regarded as the 1944 edition of the Surface Warning Set (WS). A number of decisions would have to be taken shortly.

Like the Mark IV series, the basic radar of the Mark V was common to both sets, the difference being in the aerials. Both were to have continuous power rotation, which was paramount for PPI presentation. Type 277 had variable rotation speeds up to 16 rpm with the ability to stop within 0.5 degrees of a selected bearing to 'hold' a target, or for height finding. The type 276 aerial rotated at a fixed speed of 18 rpm. Unlike previous 10 cm sets, common transmit/receive working was incorporated for the exposed  continuously spinning aerials.

The Naval Staff paper continued, stating that the tactical uses of the two sets would be:

a) surface warning.
b) aircraft warning below 3 degrees with  the type 277, below 20 degrees with the type 276;
(c) fighter interception of aircraft at elevations below 3 degrees (out to 16 miles with aircraft at 50 feet, 45 miles at
   5,000 feet).
d) With type 277 only, height finding by measurement of elevation (ie -  bracketing, not beam splitting) to an accuracy of 1 degree between elevations of 4 degrees and 40 degrees. For gunnery, both sets could be used for indication of surface or air targets. 277 was intended to  provide accurate ranges to the main armament in an emergency.

The paper also forecast what proved to be a somewhat over-optimistic range performances against various types of targets.

FITTING THE SET

The original 1942 concept stated that there should be two sets with the same electronic equipment but different aerials:

a) Type 276 (with a cheese aerial fixed in elevation horizontally) for the smaller cruisers and fleet destroyers.

b) Type 277 (with a parabolic aerial which could be set to any elevation and was capable of measuring elevation) for capital ships, aircraft carriers, larger cruisers, and all escort vessels able to bear the topweight of the larger aerial.

However the need for target indication of aircraft for gun direction became most urgent, and this gave rise to the need to extend air cover from the 20 degree range of the 276 to a 70 degree angle of elevation. To adapt developments to this new specification implied design of a new very wide fan-beam aerial and a special display unit (TIU) for preliminary target tracking. In addition, it seemed eminently reasonable at the time to assign to this target indication radar the dual role of target indication (TI) and surface warning (WS), thus greatly easing the masthead siting problems in the smaller war vessels. So the development of the type 276 aerial was dropped and the modified set, with a tipped-up aerial and renamed type 293, was substituted for type 276 in forward fitting plans.

In July 1943, the Fleet was told of the Admiralty's plans for the future fitting of centimetric warning radar. Large cruisers and above were to have type 277 for WS, and type 293 for TI. Small cruisers, destroyers, AA sloops, etc., were to have type 293 to serve for both WS and TI. To allow this to be done, all future destroyers would be fitted with a lattice foremast to also accommodate the HF/DF aerial. However, until the redesigned type 293 aerials were available, type 276 was to be fitted for TI as an interim measure in all classes.

The fitting in ships of the Fleet of the new generation of 10 cm warning sets - with their PPI's and continuous powered rotation - proceeded quickly in 1944, particularly with many new destroyers arriving from builders' yards. The most widely fitted at this stage was the surface warning type 276 with its 4 foot horizontal cheese aerial in small cruisers, destroyers and AA sloops. On the whole, the users' reaction from sea was most favourable, the maintenance staff rather less so.

How marvellous to have a PPI on the bridge, said the Senior Officer of the 39th Escort Group in the sloop Black Swan (with type 276) in April 1944, the whole value of radar being enormously increased thereby, particularly in night operations - and no less welcome in daytime! He was now able to appreciate the tactical situation instantly but side echoes were tiresome in convoy work.

MAINTENANCE AND INSTALLATION

On the other hand, owing to pressures of staff limits, accelerated development and the paramount need for rapid introduction into service without the usual preparations that would be made in peacetime, there were many technical teething troubles. ASE had to send an officer to Alexandria Egypt in March 1944 to help solve type 276 problems in Tuscan and Black Swan. Captain, Radar Training, in HMS COLLINGWOOD found it necessary to call a special meeting in September, attended by officers from sea, to discuss the many seagoing maintenance problems. Nor, apparently, was ship-fitting straightforward. In February, the Port Radar Officer at Belfast told ASE that he had had great difficulty in fitting the waveguide for type 276 into the frigate ERNE. It took the dockyard, he said, three times as long to fit type 276 into a British ship as it did to fit the American type SL (which performed exactly the same function) in the Lend-Lease 'Captain' class frigates.

FURTHER DEVELOPMENTS

The decision had been made back in August 1943 that type 276 (designed for surface warning) should only be a stop gap until it could be replaced by the type 293 giving both surface and air warning as well as being suitable for target indication and gun direction. The only difference between the two sets was in the aerial and its mounting. Trials of type 293 with its first aerial, tilted and 6 foot wide (Outfit AUR), in August 1943, proved far from satisfactory in regards to range for both surface and air targets.

Nonetheless, a fair number of destroyers were so fitted in 1944 and, in November, the Commodore (Destroyers), Home Fleet, was able to send ASE tables of the performance of type 293 in seven modern destroyers compared with the performance of type 276 in six other destroyers. In fact, the results of these somewhat unscientific trials seemed to show that there was little to choose between them. However, although this first 293 aerial was wider than the 276's (6 feet against 4 feet), it was significantly narrower in the vertical (4 inches against 10 inches) so the aerial gain was only around half that of type 276 aerial. One might have expected this difference to appear clearly in the destroyer comparison above, but it was probably masked by maintenance and tuning difficulties experienced in small ships faced with handling the early models of new and advanced equipment, more especially as fleet destroyers had not previously been equipped with 10 cm radar.

Meanwhile, trials of a new eight-foot-wide aerial (Outfit AQR) for type 293 set had proved successful. From the beginning of 1945, the aerials of all existing type 276 and 293 sets began to be replaced by the new 8 foot aerial, the resulting radar being known as type 293M.

276 SPECIFICATIONS

Power Level             : 500 KW
Wavelength               : S-band
Pulse Width              : 1.5 or 1.9-microseconds
Pulse Repetition Rate: 500
Antenna                   : Outfit AUS - Single, power rotated, 'cheese'
                                 stabilized in azimuth. Beamwidth 3.5 degrees.
                                 Rotation at 0-18 rpm
Displays                   : 'A' scope and PPI
Range Scales            : 15,000 yds (accuracy 50 yards)
                                  75,000 yards (250 yds)
                                  150,000 yards (500).

Typical ranges          : With an antenna height of 70 ft -
                                  16 nm on a battleship,
                                  14 on a cruiser
                                  12 on a destroyer
                                  10 on a corvette
                                    7 on an MTB
                                    5 on a submarine.
                                  Aircraft at 200-6000 ft could be detected at 13-17 nm.