Nimrod - The Anti-Submarine Hunting Game

" NIMROD " A/S HUNTING GAME

A hunting game has been devised at H.M.S. " Nimrod " for use in an enclosed building as an instructional device for the training of officers. The floor space available at Campbeltown consists of an ellipse whose minor axis is 30 ft. and major axis 60 ft., but this may be varied to suit any other building. The scale is 30 ft. to 2,000 yards.

2. The object of the game is to give Commanding Officers practice in the tactical handling of ships in an A/S hunt, particularly when two ships are present, and to demonstrate the finer points of a depth charge attack. In addition, it accustoms them to obtaining and giving information about the movements of the submarine, and from this and from observation of the target, to estimate the course to steer to make the point of explosion of the depth charges close the submarine on a steady bearing.

3..The game is also of value in the training of A/S Control Officers, who are inclined, from practice on an asdic attack teacher, to devote too much attention to the asdic, and have difficulty in visualising the actual position of the U-Boat in the sea. It teaches them to estimate —
a contact's probable change of bearing due to the movement of their own ship ;
the area to be swept if contact is lost ;
the most useful information to be given to, and received from, a consort assisting in the hunt.

4. In genera], experience of the game has shown that it is of great assistance in developing a seaman's eye by—
giving a physical picture of the actual conditions during all stages of the attack, including the difficult period during the time the charges are sinking ;
reminding officers that there is another ship co-operating ;
enabling officers to discover the relation between the rate of change of bearing and the angle they have to throw off for an accurate attack.

Description

5. The final design of the model submarine and ships has not yet been standardised. The following is a rough description of the gear :-‑
The submarine is circular in shape, diameter about 12 in., and surmounted by a small round conning tower. It is driven by clockwork with a speed range of 0-8 knots, and cap alter its course up to about 50°.
The two ships, 2 ft. long, with masts 3 ft. high for " hoisting " signals, are driven by electric motors, with a speed range of 0-20 knots and a turning circle comparable to that of a destroyer. A pelorous ring is fitted to enable bearings to be taken of the submarine.

6. If it is not possible to mechanise the models, they can be moved by cords marked with knots at regular intervals and pulled by operators standing at the side of the practice area, speed being governed by timing the knots by stop watch. This, however, detracts from the realism.

Operation

7. The game is played as follows :‑

The submarine is set at a given course and speed in a suitable position in the area. (Its movement is so slow that, with its circular shape, it is almost impossible to see its course and speed from the ships.)
The ships approach the submarine in, for example, line abreast, and, when within range, place themselves in a suitable tactical position for commencing a hunt.
The information that is then obtained by the Commanding Officer of the attacking ship will correspond to that available at sea—bearings and ranges of the submarine, and signalled information from the directing vessel.
When the direction of movement of the submarine has been estimated, the Commanding Officer of the attacking ship orders the approach course and speed.
The attacking ship proceeds on this course, or any new course ordered, until the time of firing depth charges. This is obtained by the Commanding Officer by a visual observation that the stern of his ship (and therefore the point of explosion of the depth charges) is directly in the submarine's path.
The ships and submarine continue on their courses and speeds until the moment of explosion, when it can be seen if a hit has been obtained.
The directing vessel manoeuvres throughout to keen, in the best position for assisting the attacking vessel.

Instruction of Ratings

8. The game also serves a useful purpose when played by or demonstrated to a newly joined S.D. (qualifying) class as it shows them the use made of the information that they are taught to give, besides assisting in their instruction in compass work.


Source - The Ant-Submarine Warfare Division Of The Naval Staff - October 1941 (British)