Gibraltar Fence (Part 2)

Part one.

Seeing another pattern of smoke floats being laid HMS Anthony came steaming back into the area. The MAD Cats radioed that they were beginning their attack run, and HMS Anthony slowed to seven knots and shifted her course a little away so as not to interfere, although she was about 300m away when Lt Wooley dropped his payload. At 1656 Plane 15 made the first MAD attack run in history, firing 23 of his 24 retro bombs. One had failed to fire.

You can see the smoke floats, and the impacts from the two planes Retro-bomb attacks. The Wake belongs to HMS Anthony. In the distance another British destroyer approaches (HMS Wishart)

Ten seconds later Lt Baker's plane passed over the contact point and he dropped a smoke float on the MAD signal, looping round he made his attack run firing all 24 of his retro bombs about 120 seconds after Lt Wooley. Seeing both planes completing their runs HMS Anthony steamed in, laying a pattern of charges on the same point as the two planes had about 20 seconds after Lt Baker.

On U-761 the crew were utterly unaware of what was going on above them. Due to several thermal layers they were having difficulty with their depth. The bow was unexpectedly heavy and so they trimmed her off by blowing air. That's when the bombs started exploding. At 1702 U-761 bobbed to the surface, as she was a lot closer than expected, upon realising their mistake the crew quickly dove her down again.

U-761 bobs to the surface

By now another destroyer, HMS Wishart had arrived and made a depth charge attack, followed closely by HMS Anthony a second time.

HMS Wishart and HMS Anthony make repeated attack runs on U-761

On U-761 all the electrics were out, and only emergency lighting was working as well as a host of other damage, including in one compartment the smell of chlorine. At 1710 U-761 surfaced and the crew immediately began to abandon ship. The Chief Engineer attached a scuttling charge to a torpedo in the stern of the submarine. Captain Geider was the last man off, however the Chief Engineer became confused and began to swim towards the stern, he was mortally wounded by the detonation of the scuttling charge, and was rescued by Captain Geider.

Abandon Ship!

At this point a USAAF Ventura and a RAF Catalina appeared and put in attacks on the submarine, at 1717 and 1719 respectively. At about 1720 the submarine sank by the stern, leaving most of the crew in the water. The majority of the crew were rescued by HMS Anthony and HMS Wishart.

U-761 can be seen in the mist from the explosions in between the two Destroyers.

Following this encounter the patrol ships covering the Strait were given a more detailed briefing on the system being used, and what to do in its presence. However on March 16th another attempt to sneak into the Mediterranean was discovered. As the MAD Cats worked out their plots a French sloop escorting a French submarine entered the area and despite requests to abort they blithely sailed through the area ignoring all attempts to communicate. However after 30 minutes they re-acquired the track and made an attack. Nearby escorts heard the impacts on the submarine and moved in to also mount their attacks. The submarine never surfaced, but with wreckage and body parts seen in the water it was judged likely the attack had been successful.

HMS Wishart rescues the survivors.

 The Germans knowing something was up, but not exactly what tried again to sneak a boat into the Mediterranean on May 15th. This time they got two Spanish fishing boats to sail above the submarine. Presumably they assumed it was some sort of acoustic detection that was catching their submarines. However the wooden boats didn't mask the magnetic field of the submarine. The submarine was promptly attacked and after some hits surface vessels were requested. The surface vessels attacks sank the submarine causing a 12 mile oil slick.

Further reading/Image credits:
U-boat Archive has a full stack of documents and photographs, which is too much data for me to reproduce here, on the incident. For example: Want to know what type of camo scheme the MAD Cats had, its all there. It includes full reports from both pilots, and interrogation reports of Cpt Geider.
 

Gibraltar Fence (Part 1)

U-761 hadn't had a glorious war. She was a VII C type U-boat built at Wilhelmshaven and commissioned on 2nd December 1942. During her first patrol under the 26 year old Captain Horst Geider she'd had a few close meetings with destroyers but was able to slip away in bad weather. Captain Geider wasn't exactly popular with his crew, he was seen as uncharismatic and overly cautious. While in port before their first patrol during a social evening, the Chief engineer had gotten a little drunk and had exchanged insults with Captain Geider. This had resulted in Captain Geider having the man arrested and court martialed, resulting in a three month prison sentence and a reduction in rank.

Captain Horst Geider

During U-761’s first patrol in winter 1943 in the North Atlantic, a period of stormy weather occurred. Cpt Geider ordered his boat to run on the surface in the face of the winter storms for several days. This left the crew soaked, five men were injured and the gun shield on the submarines quad 20mm mount was so damaged and warped the gun couldn't have been used.

At 0025 on 17 December 1943 the cook was in the forward battery compartment when the batteries exploded, injuring the cook, and releasing a large quantity of smoke. The fumes also  overcame an Engineering Officer. One suggestion was the heavy seas had prevented sufficient ventilation which had in turn caused the explosion. This caused U-761 to call short its patrol and return to base. At the base it received a retrofit, where the 88mm gun was removed and a new 37mm AA gun fitted, along with a general re-work of her smaller AA armaments.

VII C type U-boat similar to U-761's original set up

 On the 8th of February 1944 the refit was finished and she left Brest, with orders to slip into the Mediterranean, with the destination of Toulon. Cpt Geider was confident and upbeat about this, however some of his crew had served in that sea before, and the crew accepted the veterans experiences and soon became pessimistic. Around 35 U-boats had already made the passage of the Straits of Gibraltar, by approaching at night on the surface and then diving during the day and sailing through the deep water channel.

Even before U-761 reached the straits of Gibraltar things began to go wrong. Cpt Geider had complete faith in his airborne radar warning gear, and trusted it implicitly. So when he was subsequently illuminated on the surface by a Wellington bomber from 179 squadron at 0414 on the 19th, it came as a bit of a shock. Cpt Geider ordered all of the submarines AA weapons fired, however, the 37mm jammed immediately and the crew took cover. Another crew member came up from below decks and cleared the jam as the Wellington went hurtling overhead. Luckily for U-761 the Wellington had released its payload to late and the salvo of depth charges had sailed over the sub. U-761 promptly dived to safety.

 About 0500 on the 24th U-761 took its final bearing and submerged, at least twice more Cpt Geider raised his periscope to check his position. This would later be blamed by the crew for the fate that befell them. For U-761 was approaching its place in the history books, and heading directly towards a pair of MAD Cats.

The MAD Cats in this case belonged to the USAAF's 63rd Patrol Squadron. They were Catalina flying boats fitted with a Magnetic Airborne Detector, or MAD ("Anomaly" was used after the Second World War). Two of the squadron’s planes were on a continuous circuit over the deep water channel in the Strait of Gibraltar looking for any German submarines. This was known as the Gibraltar Fence. They'd been operating for over a month without a hit. Then at 1559 plane number 15 flown by Lieutenant Wooley got a signal. He was joined by another MAD Cat flown by Lieutenant Baker in plane number 14. One of the crew in Lt Baker's plane had a camera with him, and documented the rest of the action.

Both pilots began to fly a cloverleaf search pattern, on each pass they'd drop a smoke float which would mark the position of the strongest return on the MAD. After several passes you'd get two lines of smoke floats indicating the submarine’s course and speed. The pilot then could set the MAD to automatically fire its bombs on the next pass, or it could be done manually.

Lt Wooley performing a Cloverleaf patten. You can see the line of smoke floats dropped to mark the course of the U-761

 One oddity was the bombs used; as the MAD would fire when the signal was strongest then the bombs would have forward momentum and fly over the target. To prevent this the bombs known as retro bombs or officially as "Contact VAB MKVI" were used. These were rocket propelled bombs that fired backwards off the planes wing at around 100 knots. This meant that they had a forward speed of effectively nil, and would fall straight down. Each 65 lb retro bomb had a contact fuse, so if they touched the submarine they'd detonate.

As the two planes circled laying smoke floats on their track a nearby destroyer HMS Anthony approached to see what the fuss was about. However the Captain didn't know of the existence of the MAD system or how it worked. Having an ADISC contact she moved to attack, however her presence meant the MAD system got scrambled. To make matters worse the MAD cats had to fly at just 50 feet, and so were in danger of a collision with the destroyer which meant that both pilots had to break off their search pattern.

HMS Anthony arrives on scene

 HMS Anthony announced its intention to attack, but lined up on the wrong end of the smoke floats. When it was informed it was attacking the wrong location HMS Anthony turned about and steamed for the head of the line. However she didn't attack and her wake scattered the smoke floats already laid.

When HMS Anthony cleared the area, after some choice words from the Catalina's, Lt Baker then ordered Lt Wooley to begin a spiral search pattern, while he  performed several more cloverleaf patterns. After these became fruitless Lt Baker joined in the spiral search pattern. At 1645 their patience was rewarded with another MAD hit at about one mile south-southeast of the previous locations.

 The hunt was back on.

Part two.

Image credits:

U-boat.net, uboatarchive.net and uboataces.com