Officer who captured the first code books and documents for a German Enigma machine off Norway in 1940 

---

Commander Alec Dennis, age 91, died in July 2008. He captured the first documents and code books for a German Enigma machine when a lookout on the destroyer Griffin off Norway in April 1940 spotted a trawler with a large painted Dutch flag.

As Griffin drew close it became clear that a boat at the stern was only a canvas mock-up, and when Dennis leaped aboard he was confronted by a dazed figure who at once said: "German ship". The mock-up covered a gun, and two torpedo tubes were barely covered by fishing nets. When the rest of Dennis's party scrambled aboard, the German crew were brought on deck to face loaded .45s. Making no effort to resist, they instead threw overboard confidential books, ciphers, charts and a machine.

The books did not sink at once, and Gunner Florrie Foord dived from Griffin's quarterdeck to recover them. Dennis put a man on the bridge of the trawler Polares but he stumbled and let off his revolver, which had the good effect of cowing the Germans on the well deck who could not see what had happened. Dennis was inspecting the ship to ensure that she was not being scuttled, when a German crewman warned him in English that the hatch leading to the magazine was booby-trapped. After making this safe and sending most of the Germans aboard Griffin, he shaped course for home.

"This was not all that easy as our initial position was uncertain," Dennis recalled, "and I soon discovered all the charts and navigational equipment had gone overboard.  "Off we went, me on the bridge with a German helmsman and a petty officer in the boiler room with a number of German stokers who seemed willing enough. We were slightly outnumbered but kept alert and close to our weapons. "The trip home was great fun. A big fat Bavarian chef cooked us some huge meals of bacon and eggs, which Polares had taken on from Denmark. We painted out the Dutch insignia and couldn't resist flying the White Ensign over the Swastika." After two days the captured boat made a triumphant entry into Scapa Flow.

Dennis had promptness, efficiency and could 'chew glass' .

With the documents recovered from the sea and another found in Polares giving the procedure for setting the scrambler of an Enigma machine, Alan Turing was eventually able to read Enigma at Bletchley Park. Dennis was mentioned in dispatches for his promptness and efficiency in capturing an enemy ship. But it was more than 60 years before the historian Hugh Sebag-Montifiore explained, in a series of late night telephone calls, the importance of his capture.

John Alexander Jeffreys Dennis, known as Alec, was born on February 19 1918, the son of a doctor. His mother's family included John Jeffreys, midshipman of the boat which carried Bonaparte from St Rafael to the frigate Undaunted in 1815. Alec was a child of empire, scarcely knowing his parents when they returned from India just before he entered Dartmouth in the Rodney term of 1931. There he played football and rugby in the firsts and in the college squash team.

Dennis served in the battleships Rodney and Resolution and the Admiralty yacht Enchantress, before joining the cruiser Suffolk in the China Fleet. After courses in Portsmouth he joined Griffin in January 1939, serving continually in destroyers throughout the Second World War. Dennis was promoted to Lieutenant-Commander Johnny Lee-Barber's first lieutenant, still in Griffin, and, in 1941, awarded the DSC for gallantry and distinguished services in Greek waters. Dennis was first lieutenant of the destroyer Savage at the Battle of North Cape, when he was again mentioned in dispatches for his part in the sinking of the German battleship Scharnhorst. In late 1944 he was given his first command, the destroyer Valorous, in which he earned a third mention, for gallantry and devotion to duty in seeking out E-boats and beating off a series of attacks on a convoy.

Still only a lieutenant, Dennis returned to Norway in May 1945 to liberate Kristians  and to take the surrender of 26 U-boats and 15,000 German soldiers. King Haakon VII awarded him Norway's Liberty Medal. In June 1945 he took command of Tetcott, destined for the war in the Pacific, but got no further than Gibraltar. With the return of peace he was given a series of minor jobs before retiring in 1957.

Dennis and all his ships survived the war unscathed, though he reckoned he had been subjected to more dive-bombing attacks than many others. In later life, however, he suffered from asbestosis, which he probably picked up while in destroyers. He emigrated to Canada, where he joined a glazing firm in Montreal, rising rapidly to be offered a place on the board in Toronto. But he resigned, gained a teaching certificate and taught for 10 years in Vancouver before retiring to cultivate his rose garden. He was also amused to have received a Russian award which entitled him to free bus travel in the Murmansk region, and a confidential report which said he could "chew glass".

Having witnessed the torpedoing of the battleship Barham at close range by U-331 in November 1941 he became friends with its captain, Hans-Diedrich von Tiesenhausen, who settled near him. Alec Dennis married a cousin from New Zealand, Faith Hammond, during two days of shore leave at Llangollen in January 1945: he read his own banns onboard where no one dared challenge them. He claimed that the marriage was arranged by their mothers; relatives said that the match would not last. But it did, until Faith died in 2001. Dennis died on June 29, and is survived by a son and a daughter.

© Copyright of Telegraph Media Group Limited 2008