Hi Vinny,

These anti-torpedo nets were referred to (by the Brits) as the “Admiralty Net Defense” although they were used on American, Canadian & British merchant ships that were equipped to deploy them during WWII. I am not certain who invented them though. They were probably used on other allied merchant ships too but I don’t have a source to prove that. At any rate they weren’t used all that much, especially as the war progressed and the convoys were better protected by an adequate number of properly equipped (ASDIC, radar, Huff/Duff etc.) escorts and air cover. Note that they were used or at least tried out during WWI.

They were effective but as you will see they had serious drawbacks, not the least of which was that the ship’s crews hated to fool with them as they were quite labor intensive to deploy and recover. I have talked to American merchant seamen who served on vessels that deployed them and nobody had anything good to say about them.

There were cases of ships that deployed them being sunk by torpedo despite the nets because they didn’t always cover the entire side of the ship and they didn’t protect the ship from torpedoes fired from directly in front of or behind the ship. There were however cases where ships were saved by the nets and at least one case I heard of where the ship attacked didn’t even know it had been attacked by a U-boat until they retrieved their nets and found the torpedo tangled up in it.

There is a rare photo of a merchant ship deploying its net defense along with a nice description of the problems associated with it at: [homepage.ntlworld.com]. Just scroll down to get to that part. Note that a paravane on a merchant ship was also rare (this is the only photo I have ever seen of a merchant ship with one).

Also see: Blair, Clay Jr. Hitler’s U-boat War – The Hunters, 1939-1942. New York: Random House, Inc., 1996. ISBN: 0-679-64032-0. Copyright: Clay Blair, 1996. Page 510-511:

“Among the ships in the convoy, was the 8,000 ton British tanker EMPIRE CELT equipped with a new and experimental anti-torpedo device known as the Admiralty Net Defense. The device consisted of huge rolls of strong steel “nets” which could be streamed from 50 foot poles over the starboard and port sides in times of danger or when sailing alone. During controlled tests, the nets had stopped British submarine torpedoes, but this voyage was the first “combat” trial of the device. Although the nets could not be streamed at speeds greater than 9 knots and they were difficult to handle and had to be replaced after each voyage, their advocates believed them capable of providing about 50 to 60 percent protection for freighters and tankers. The Admiralty Net Defense project manager, C.N.E. Currey, and a senior American submariner, George C. Crawford, were embarked on the EMPIRE CELT to oversee and observe the combat trial.
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Next two Type IX’s closed to attack: Rosin in U-158 and Wattenberg in U-162. Rosin hit and damaged a tanker. Then (24 Feb 1942 - KD) he and Wattenberg probably fired simultaneously at the tanker EMPIRE CELT, which was in the process of streaming her Admiralty Net Defense (only U-158 was credited with the hit – KD.) A torpedo broke through the net and hit amidships, making a gaping hole. She fell out of the convoy and broke in half. The bow sank.
A tug from Newfoundland rescued forty-five men from the stern, including Currey and Crawford, and attempted to tow it to St. John’s but the effort came to naught thirty-five miles short of the goal. The failure of the combat trial was a “grave blow to the Admiralty Net Defense program”, a British authority wrote. Nonetheless, the Admiralty fitted numerous ships of 8,000 tons or more with the device.*

*The Allies equipped 768 merchant ships with net defense. A total of twenty-one ships fitted with nets were attacked by torpedoes during the war. The nets deflected ten attacks, but five ships were damaged and six were sunk.”

Note that Blair isn’t always a reliable source and I rarely quote him.

Also note that the Admiralty Net Defense wouldn’t protect a ship from a torpedo with a magnetic pistol set to run under the ship. Additionally special versions of torpedo pistols that had net cutters were developed but I don’t think they were ever issued to U-boats. I think they were probably for aircraft-dropped torpedoes for use against ships in harbor.

Hope this answers your question.

Regards,

Ken Dunn