The Gathering Storm. Geirr Haarr
attention was paid to training the officers and commanders to understand what the instruments told them and how to use the information tactically. There was a delicate chain from the Asdic operator to the captain and his team on the bridge, and from them to the depth-charge operators on deck. Unless all elements of this chain were fine tuned and aware of their dependence on the others, day and night and in all kinds of weather, the weapon system was less than fully efficient. Knowing where the U-boat was, even if detected by the Asdic, was far from easy and required quick three-dimensional thinking by the captain – all the more so as the Asdic lost contact as the escort increased speed, closing the distance to deliver the attack. In difficult Asdic conditions, or when the water was disturbed by multiple depth-charge explosions, the chance of a U-boat escaping a single A/S vessel was relatively good.
The use of several ships in cooperation, one keeping Asdic contact while the others attacked, increased the efficiency of the A/S vessels significantly, but was a tactic that also had to be learned and exercised.
Few in the Royal Navy were proficient in A/S warfare in 1939, and when the ranks swelled with a large number of RNVR, draftees and volunteers, the overall competence did not increase. Intense practice was needed, not least on the after deck where reloading of the depth-charge throwers was found to be disturbingly slow.3
Hardly any Asdic exercises had been conducted under conditions close to reality. In the exercises that were held, it was often found that the Asdic failed and even when it did work, it had a number of weaknesses. British submarine captains found it relatively easy to escape Asdic-equipped destroyers, once they learned how the apparatus worked and how the A/S crews responded to the information it gave them.4
By overestimating the efficiency of Asdic and not appreciating its deficiencies and the need for adequate training, the Admiralty to a large degree predestined the Royal Navy to start the war with a severe handicap. The fact that some U-boats were sunk seemed to confirm the belief of the Admiralty that a convoy system backed up by Asdic, aerial reconnaissance and more effective depth-charges would all but neutralise the submarine threat. That the sinkings were significantly overrated and that most U-boats actually got away was dismissed, as was the fact that most of the Asdic sets were fitted in destroyers intended for fleet-work and not convoy escort. Likewise, it was not appreciated that surface attacks at night would render both Asdic and aircraft useless. Few believed at this stage that high-quality radar and radio direction finding would be as important as Asdic in overall convoy protection.5
On 20 September, destroyers Imogen and Ilex were patrolling south-west of Land’s End under the command of Commander Henry Pawsey on board Keith. Lieutenant Robert Ewing was first officer of Imogen. His diary is revealing of the confidence some officers carried regarding their ability to defeat the U-boats:
At 7.20 p.m. we received from Flying Boat: ‘Am over enemy submarine in pos. 49° 42' N, 07° 25' W. Keith made to Ilex: ‘[Will] proceed to search for S/M on or near surface. Patrol independently during the night to eastward of 8° 30' W, rejoining me in 49° N, 9° W. Why in God’s name he did not take all of us to search I cannot understand. We were doing nothing in particular and sending one destroyer to find a submarine after half an hour’s delay is fantastic. [. . .] He is obviously out of touch with things. [. . .] Keith reaped his reward from C-in-C Western Approaches in the following: ‘When report of U-boat is definite, your whole force should be sent and remain until she is destroyed.’6
C-in-C Western Approaches Admiral Martin Dunbar-Nasmith was one of the first to realise the deficiencies of the A/S systems, and he issued a series of instructions on 25 September to the Anti-Submarine Striking Forces operating under his command. It was essential to sink U-boats and kill or capture German submariners. One of the paragraphs read:
When contact is obtained, the U-boat is to be hunted continuously and relentlessly until destroyed. Should contact be lost, the search is to be continued day and night until is regained. No contact is ever to be relinquished until it is considered certain that the U-boat has been destroyed, or it has been established the contact was a ‘non-sub’.7
Whenever an attack on a U-boat was reported it was assessed by a committee of the Anti-Submarine Warfare Division and given an official status as sunk, damaged or even ‘non-submarine’ at times. The NID made aggregated valuations based on these assessments and independent information available to them. Surprisingly, this created a serious contention between NID and the First Lord, with Churchill wishing to announce measures of success while NID saw the need for an accurate assessment as the basis for tactical and operational amendments. Still, even NID overestimated the number of U-boats actually sunk. At the end of 1939, Churchil implied that some forty U-boats had been sunk so far in the war, NID held a maximum of twenty-five, while the actual number was nine. By 10 March 1940, NID estimated a maximum of twenty-one sunk versus the actual number of sixteen (see Appendix G).
At the beginning of the war, the only A/S weapon available to the Royal Navy was the depth-charge. This was little more than a free-sinking cylindrical container filled with around 330 pounds of high explosive, originally Amatol, later changed to Minol, a mixture of TNT, ammonium nitrate and powdered aluminium, which had a greater explosive effect for the same weight and volume.8 The depth-charges were detonated by a firing pistol activated by hydrostatic pressure with fixed settings at fifty-foot intervals from 50 to 500 feet (15–150 metres).
The Royal Navy Type D Mark VII depth-charge, which was standard by 1939, had an initial sinking speed of 2 metres (6 feet 6 inches) per second, increasing to 3 metres (10 feet) per second at depth. Improved sinking rates were obtained by adding cast-iron weights to the charges. When it was realised that the U-boats went deeper than expected, improved hydrostatic triggers later also increased the maximum triggering depth. In theory, if the charge exploded within 15–25 feet from the hull of a U-boat, the submarine would be destroyed. At more than twice that distance, damage could still be significant, often forcing the boat to surface.
Usually, the depth-charges were dropped in a pattern of five if a U-boat had been identified. Three were dropped or rolled from the stern in succession, some 150 feet apart, while two were fired from depth-charge throwers, one on each side amidships, to a distance of 150 feet from the ship. These two were timed to hit the water at the same time as charge number two was dropped from the stern. The T-shaped depth-charge holders were manhandled into the throwers, whereafter the charges were set in place by a block and tackle. It was hard work, which meant that time was needed to prepare each attack. Not all trawlers or auxiliaries had depth-charge throwers installed from the start.
Pink Gin
There is no doubt that the failure of the Admiralty to accept the need for and provide adequate numbers of suitable escort vessels with satisfactory A/S capacity in terms of Asdic, weapon systems, tactics and training in time, was a serious blunder. With the exception of a limited number of multi-purpose sloops, no A/S escort vessels were built by the Royal Navy between the two wars; the destroyers were built for a different purpose, with A/S capacity as, at best, a secondary task.
Depth-charge ready for action on board the destroyer Ardent. The cylinder on top of steering-guide is the explosion chamber, set off by the rope attached to the firing wedge and pistol on its top. (M Sellick collection)
The explosive effects on the surface were also huge and the A/S vessels frequently suffered damage. (Author’s collection)
Having been deployed singly or in small groups at overseas stations around the world, a number of the sloops were called back to Britain during 1939. Most of them needed a spell in the yards before being assigned to convoy escort and when deployed, as with the corvettes later, they were found unsuitable for sustained work in the Atlantic under winter conditions. The Hunt-class destroyers, designed during 1938 in an attempt to provide a seagoing escort for both warships and convoys, were few in numbers due to yard capacity and they did not really stand up to sustained deep-sea convoy