The following has been extracted from the Royal Navy's BR1669 Handbook of Depth Charges and Equipment - General and Operational Notes, 1943. Some of the information, notably the table showing enemy submarine losses, is probably suspect. Nevertheless, this provides good background to the introduction of the depth charge into the RN.
1. The idea of the depth charge, together with many other possible forms of attack on submarines, originated before August, 1914.
2. On the outbreak of hostilities the only anti-submarine device available was the single sweep. This consisted of a solid metal kite containing 100 lbs TNT, kept at its depth by a skid on the surface and towed by a length of armoured electric cable. It was fired by order of the captain.
3. An improved sweep was under development and became available in the winter of 1914. This consisted of nine 70-lb TNT charges towed astern of a destroyer, or trawler. A loop of cable was towed astern and in the bottom part of the loop were the nine charges, while on the top part were 12 floats. The whole was kept at its depth by a kite. The two ends of the loop were connected to a towing beam; as soon as the towing beam swung, the charges were fired by a hand standing by for that purpose. This device did not last lon in Grand Fleet destroyers, 630 lbs of TNT primed and fitted on the upper deck was considered too dangerous. Launching entailed reduction of speed, and recovery stopping for a long time. Trawlers, however, continued to use it. One submarine was sunk by this device.
4. The high speed sweep, consisting of a paravane, containing 80 lbs of TNT towed by an armoured electric cable, was developed by Lt. Burney. This was fired automatically as soon as the submarine touched the paravane or towing cable, or by hand from the bridge. This device was quick to stream, could be towed up to 25 knots, and recovery was reasonably simple. It was still afloat at the end of the war, with four submarines to its credit.
5. In October, 1914, the Commander-in-Chief, Grand Fleet, asked for a depth charge, in the form we now know it. Development started in November, 1914.
6. In December, 1915, the following depth charges were issued or under development:-
| Type | Charge and Weight | Depth of Firing | How Operated | Special Features | History |
| A | 32 ½ lbs GC | 40 ft | mechanically |
- |
Adapted from "Vernon" boom. |
| B | 32 ½ lbs GC | 40 or 80 ft | mechanically |
- |
Adapted from "Vernon" boom 2nd type issued |
| C | 35 lbs TNT or Amatol | 40 or 80 ft | mechanically |
- |
Adapted from aeroplane bomb |
| C* | 35 lbs TNT or Amatol | 50 ft | hydrostatic |
- |
Adapted from aeroplane bomb |
| D | 300 lbs TNT or Amatol | 40 or 80 ft | hydrostatic | primer safety gear | Special design. For large and fast vessels. |
| D* | 120 lbs TNT or Amatol | 40 or 80 ft | hydrostatic | primer safety gear | Special design. For small or slow craft. |
| E | 100 lbs TNT or Amatol and 16 1/4 lbs GC | 40 or 80 ft | mechanically |
- |
Adapted from "Vernon" boom. for motor launches, whalers, sloops and patrol craft. |
| F | 70 lbs TNT | 50 ft | hydrostatic |
- |
For use with bomb thrower. |
| Cruiser mine | 250 GC | 45 ft | hydrostatic |
- |
Adapted from service mine. |
[GC = gun cotton]
7. Of these, types "A", "B", "C", "F", and cruiser mine were in general use. Type "C*" to be ordered. Type "D" about to be issued. Type "D*" under trial. Type "F" trials nearly completed.
8. The mechanical operation mentioned above consisted of a float connected to the mine by a lanyard, the depth of firing being regulated by the length of the lanyard. The pistol was of simple pull-out type. Later, a Type "G" depth charge containing 35 lbs of TNT or Amatol was adopted for dropping by hand.
9. The Type "D", designed in 1915, is still the standard type and has been very little altered from its original design, the pistols being developed to give different firing depths. Primer safety gear was abolished, but will shortly reappear. A good example of sound design in the first place, standing the test of time for 28 years.
10. Thirty-five submarines were definitely destroyed by depth charges.
11. In November, 1918, the following ships were fitted with depth charges:-
| TBDs and Leaders | ... ... | 437 |
| "P" Boats | ... ... | 63 |
| Sloops | ... ... | 101 |
| Trawlers | ... ... | 285 |
12. Three hundred and fifty-one TBDs and about 100 other vessels were fitted with depth charge throwers.
13. The table below gives the approximate average monthly expediture of depth charges in the Great War, compared with this war:-
| 1916 | 100 | 1940 | 1,700 |
| 1917 | 200 | 1941 | 1,000 |
| 1918 | 500 | 1942 | 1,300 |
14. A total of 16,500 was expended during the Great War; in the first quarter of 1943 the figure was over 8,000.
15. The following is a record of the major successes against submarines from August, 1914, to November, 1918:-
| Weapon | Class of Ship | Definitely Destroyed | Serious Damage | Slight Damage |
| Depth Charge | Man-of-War | - | 6 | 3 |
| Depth Charge | Destroyers and Patrols | 35 | 85 | 182 |
| Ramming | Man-of-War | 5 | 2 | 1 |
| . | Destroyers and Patrols | 9 | 6 | 5 |
| . | Merchant Vessels | 4 | 8 | 24 |
| Gunfire | Man-of-War | - | 1 | 7 |
| . | Destroyers and Patrols | 13 | 23 | 88 |
| . | Merchant Vessels | - | 7 | 96 |
| . | Decoy Ships | 11 | 42 | 43 |
| . | Armed Smack | 1 | 8 | 1 |
| Mines and Mine Nets | 43 | 28 | 30 |
16. The original method of release was from a chute over the stern operated by hand. Later hydraulic release operated from the bridge was fitted. In late 1917, rails were fitted in submarine hunting and local flotillas to enable the length of the barrage to be increased. At the same time, depth charge throwers were introduced to increase the width of the barrage.
17. It must be realised that the only method of location of submarines was by hydrophones, which were not very reliable. The usual method was to attack the position were a submarine was seen to dive or fire torpedoes.
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