Just like radar, the resolution of Asdic improves as the transmitted pulse is made shorter. If the sound beam is narrowed, the capability for distinguishing two targets at different angles improves. This is known as angular resolution. Range and effectiveness of sonar are affected by many factors. The water surface and sea bottom are natural limits to the propagation of sound. In some cases, layers of water can stratify at different temperatures. This temperature inversion can cause the acoustic beam to be deflected toward the bottom, where it will be reflected upward to the surface, down again, and so on, rendering the sonar useless. Sound travels around 4,800 feet per second in 40 degree F sea water as compared to 1,100 feet per second in 40 degree F air.

Turbulent areas of water may scatter the beam, causing the signal strength to fluctuate and distorting the reflections. The water may also absorb the sound energy, transforming it into heat; this heating effect increases rapidly as the transmitting frequency is increased. The velocity of the sound wave and hence the accuracy of distance measurement is affected by the temperature, depth pressure, and salinity of the water. Sound velocity rises in direct proportion with these parameters. Acoustic noise limits the range of Asdic, because it masks the reflected signal. Such noise may be caused by wave action, aquatic animals, or other surface craft. The speed of the ship is also a limiting factor as the water passing by the Asdic dome creates its own sound energy and can hide any weak echoes.

A problem with early sonars (ASDIC's) was their limited search ability as the oscillator projected its cone shaped beam at an angle of 10 degrees from the horizontal. Below the beam of acoustical energy was a considerable amount of dead space that would permit the target to elude Asdic. If the enemy escaped detection, depth charges had to be dropped by estimating the target's position. Wartime experience showed that this dead zone was even larger than envisioned because submarines could dive far deeper than was originally thought possible. As a result, a clever submarine commander could often manoeuvre out of harm's way. Once contact was lost, it was very difficult to re-establish.

When operating in conjunction with other detection ships, it was very important that all the operating ASDIC's were tuned to different frequencies. If an operator was negligent of this, a transmitted pulse from another ship's Asdic would be detected as an extremely loud echo on another set. The operators' ears would experience the threshold of pain as the amplified echo thundered in his headphones. The Asdic's developed during the war operated on a number of discrete frequencies between 14 and 22 Kcs. Power output of oscillators was inversely proportional to the operating frequency. Many operators favoured operation in the 14 to 15 Kcs range because they believed that greater ranges could be obtained as contrasted by operating at 18 to 20 Kcs. It was well known that greater ranges could be had at 10 or 12 Kcs, but that meant increasing the oscillator size. It was a trade off.

ASDIC set designs generally fell into one of two categories depending on the type of ADSIC dome. In the first type, the oscillator was housed in a dome fixed to the bottom of a vessel near the bow. The second type was housed in a retractable dome that could be positioned inside a chamber built into the hull of a vessel. Normally, this last type was fitted into vessels whose operations could damage an unretracted housing. Destroyers, which could damage their domes while operating at high speeds, and minesweepers, which could foul Asdic domes with their sweeping gear, were typically fitted with a retractable dome. To protect Asdic sets from ice damage, the RCN decided to fit all new vessels with retractable domes in mid-1942. When the dome was in the housed position, it precluded using ASDIC. Corvettes, Fairmiles and converted yachts that only incorporated the most basic of necessities, did not have retractable domes.

As a result, many of these ships sheared their domes by striking logs or chunks of ice off the coast of Newfoundland. These fixed installations were not very successful but it was better than not having any system. When corvettes discovered a U-boat lurking in the depths, it became practice for the corvette to try to drive the U-boat underwater where it was slow and nearly blind, then return to the convoy. Trying to overtake the U-boat was pointless since the surface speed of the U-boat was slightly higher than that of a corvette. Later on, design improvements produced a sword shaped oscillator whose physical appearance resembled that of a sword and the angle from the sword to the bow could be altered to detect deep targets. In some Fairmiles, the oscillator was fixed to the hull and to train it on a new bearing, the ship would have to be turned. The standard procedure was to steer on the contact while altering course in a cast off fashion and back on again until the ship was able to drop depth charges.

From its inception in 1917 until the late 1940's, the detection range of ASDIC remained at basically 2000 yards. True, during World War II, there were refinements in fire control and depth measurement, but the range remained much the same. If conditions were ideal, a target at a range of 3000 to 4000 yards could be detected and but that was the absolute limit. Contrast this to today's hydrophone technology that can detect the propeller noise of a diesel electric submarine at distances of 100 nm. A modern system can also identify the class of submarine by comparing the hydrophone signal to a pre-loaded signature in the memory of a computer.

Tactically, an ASDIC that only produced a narrow beam was very useful for attack, but not for search, since it could not look rapidly in many directions. It was not until the end of World War II that 'true' search sonar was introduced into the world's navies.