HMS Alliance Tour - Attacking, Radar and Radio

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Attacking

The plot was used at action stations to correlate periscope, sonar and radar bearings and ranges to give the enemy’s course and speed.

Another type of display, the Time-Bearing Plot, is hung vertically in the passageway. This was used to display contacts on long range sonar which could detect targets out to ranges in the order of 100 miles but had a relatively poor bearing accuracy and no facilities for differentiating one kind of noise source (recorded visually) from another: the Time Bearing Plot aimed to resolve this information into a meaningful pattern.

The shorter-range sonar, mounted in the large dome on the bow, was much more accurate. It also enabled the operator to listen to a target and judge what kind of vessel it was and, from counting the propeller revolutions, to estimate the speed.

All this information had to be carefully integrated to classify and identify a target and to calculate range, course and speed. The torpedo firing solution was worked out by the Torpedo Control Calculator at the forward end of the Control Room, which generated the angling relayed to the torpedoes in the tubes.

The Masts

Radar and Radio

The radar and radio offices are at the after end of the Control Room. Radar could be used at periscope depth (with a periscopic mast) but the aerial itself was liable to detection and had to be raised circumspectly. When dived, Alliance could receive radio messages submerged at periscope depth on the special submarine VLF (Very Low Frequency) broadcast; no aerial had to be exposed above the surface.

However, an aerial did have to be raised to transmit signals on HF frequencies; these signals were liable to reveal the submarine’s position by D/F (Direction Finding) equipment in ships and onshore so only very important signals such as enemy sighting reports were transmitted on patrol.

Warning of aircraft using anti-submarine search radar was given by a special aerial used when snorting when, especially at night, an aircraft might not be sighted through the periscope.

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