SM U 77

SM U 73 (of the same type as U 77) in dry dock

On, or just after 7 July 1916 95 in 100 metres

Built: 1915 by AG Vulcan, Hamburg

Construction: steel 755 grt (displacement, surfaced), type UE 1 u-boat, length 56.8 m, beam 5.9 m, draught 4.86 m (height 8.25m)

Propulsion: twin screw, 2 x 6-cyl diesels 900 HP each, 2 x electric motors 900 HP each

Armaments: 2 x 50cm external torpedo tubes (bow and stern) , 4 torpedoes, 1 x 8.8cm SK L/30 deck gun, 38 mines

The U 77 was a type UE 1 ocean mine laying boat from WWI, 10 boats of this type were commissioned and they were extremely successful raiders. The UE 1 boat, U 73, was responsible for the sinking of the 48,000 grt SS Britannic in November 1916 and the U 75 laid the mines that sank HMS Hampshire in June 1916 , claiming the life of Lord Kitchener. The U 77 was not so successful.

She was ordered on 9 March, 1915, launched 9 January, 1916 and commissioned 10 March. During May and June she was at Kiel school and first entered the North Sea together with U 76 on 29 June when she joined the 1st Half Flotilla.

On 1st July, she was given orders for her first patrol, which was to proceed to the Moray coast to lay mines between Kinnaird Head (Fraserburgh) and Knock Head (Whitehills, just west of Banff), an area where it was believed naval vessels would pass, on their way to the deep water base at Invergordon. We were able to obtain a translation of her secret orders for the patrol.

Top Secret

Leader the U boats Wilhelmshaven 1st July 1916

Officers orders

For U 77

A. News

1.) According to secure news traffic of war ships takes place between Kinnaird Head and Cromarty South of the mines of Meteor.

2.) Experiences of submarines concerning surveillance and so on look at K.d. U.89 and 125/16

3.) U 47 stated that Sunday is ideal for operations at the coast because at the end of the week the local fishing boats are not at sea.


B. Assignment

Course from Kinnaird Head to Knock Head at a distance from 2 to 4 sm from the connecting line of these points contaminate with mines.

The mines may not at all lie to the east of the degree of longitude Kinnaird Head.

Depth timing or adjustment 7 m under high-water.

C. No trade warfare

To the High sea forces 1. U.Halbflottille U 77

She left Heligoland on 5th July under the command of Kaptlt Erich Gunzel with a crew of 33 and a load of 34 Type II E-mines onboard. She did not return from her mission and there was no trace of her crew, all are presumed lost. We know that she managed to reach her area of operations and laid some of her mines, they were found and destroyed by the navy on 26 July (this was reported in the Bi-monthly Minesweeping Report). None of her mines caused any damage to shipping. There were no British naval reports of engagement with any U-boats at that time so it was assumed that she had been lost in an accident while laying her mines, or on her voyage home.

The last sighting of her was at 4pm on 7 July, 1916 when a U-boat, presumed to be U 77, was spotted heading north, slowly about 50miles east of Kinnaird Head. For a period in the late nineties, she was thought to have been found off Dunbar, south of Edinburgh, but that wreck has, since 2005, been generally accepted to be that of the U 74. So, her whereabouts and actual cause of sinking have been a mystery for nearly 105 years.

Our team were aware of her existence but we had no reliable position for the wreck and, given she could have been lost on her return from patrol, it wasn't even clear that she was in the Buchan area. We did have one mark, which a side scan survey had indicated as a possible submarine, about 20 miles ESE of Kinnaird head but when we dived the wreck, we identified it as the Subworker, a steam dredger which foundered in 1913. We had pretty much given up hope of ever finding the her remains when, one rainy winter's day in early 2020, our old friend and expert wreck researcher, Kevin Heath, got in touch to inform us that he and Michael Lowrey had reviewed the available information on the U 77 and felt he had a reliable suggestion for her position.

Kevin and Michael had pieced together some key information that we had missed;

  1. Her orders were to lay mines in a very specific area, bounded east by Kinnaird Head and west by Knock Head, and by 2 miles north and 4 miles north of the connecting line between the two points.

  2. She would have laid her mines in depths of 100m or less. There are many deep trenches in this area so her mine laying positions would have been limited to the shallower sections.

  3. Kevin and Michael were able to obtain locations for the mines which had been discovered in the area after the 7th July. There were only 9 mines found, so 25 were unaccounted for. It was clear that she had not finished her mission and would likely be still in the area, furthermore with so many mines unaccounted for, it added weight to the theory that she had been lost to one of her own mines in an accident, possibly while laying the 10th mine.

  4. A UK Hydrographic Office report (possibly from 1965), noted a wreck in the area giving off oil. It was more accurately side scanned in 1987, and a wreck 47m long and 6.4m high was seen with a prominent "funnel" amidships. Kevin suspected that the "funnel", typically one of the first components of a wreck to collapse and therefore surprising to be still in place, could, in fact, be a conning tower. Furthermore, the dimensions of the wreck tie in very closely with those of the pressure hull and height of a type UE 1 u-boat.

The wreck noted in the Hydrographic Office report was adjacent to the lines of 9 mines that the U 77 had successfully laid and within the 100m depth of her limit of mine laying operations. There are no other reliable marks in the area. So if she had been sunk by her own mine, this mark is her most likely position.

Super wreck detective work!

In fact, this wasn't a new wreck position for us. We had been aware of it for many years but it looked quite small, we assumed it to be a steam trawler and, given its depth and its distance from Peterhead (2 hours steaming) we had prioritised other, more interesting and less challenging marks for investigation. We had failed to appreciate the significance of the midships "funnel" comment on the survey report and we were not aware of the specific details of the U 77 area of operation.

However, armed with this new research, and the thought that we might be able to solve the 105 year old mystery of the U 77, we prioritised the mark for investigation and possible diving in 2020/21. It would be a serious undertaking though, our deepest wreck to date. Careful planning would be required together with work up preparations, surface support and the right weather and sea conditions.

The 2020 season did not allow such grand adventures, but in 2021 we targeted the wreck for exploration from the surface - despite our faith in Kevin and Michael's research, we did not want to risk a dangerous dive to 100m to find an old trawler. We made two attempts to film the wreck from the surface using a borrowed ROV operated from Jim's RIB - both attempts failed with no video to show, and the near loss of a £7,000 ROV.

However, we had better luck with a borrowed dropcam (an underwater camera and light on the end of a long cable, hooked into a surface video display). Naomi Watson and Jim headed out on 2nd September in flat calm seas to make a third attempt to film the wreck. It was not easy but we were able to get some footage which confirmed the wreck to be of a submarine - and it can only be the U 77.

She lies on a mud seabed in 100m running approximately east/west, in poor visibility (unexpected for a Moray coast wreck) and wrapped in nets and ropes. From the sounder trace, we can see that the westward end of the wreck is intact but the eastward end is broken up and there is a debris field here. We are not yet certain which end is which, but bow to the west and stern to the east would be consistent with the theory of her loss was caused by one of her own mines exploding in, or near, her stern minelaying chute (this is also how U 74 met her fate). The stills from the video show the pressure hull and outer hull, with penetrations for possibly the depth gauge equipment, the hull is curved to the seabed and there looks to be torpedos or pressure vessels lying around her on the seabed.

Poor weather and engine problems have affected the tail end of our 2021 season and we have not dived since July. The extra information about the nets, mud and poor visibility means that this will be an even more challenging dive than we had thought. We hope 2022 will bring the conditions and opportunity to dive and explore this important piece of history.


Special thanks to Michael Lowrey and Kevin Heath for their help in finding this wreck and also to Ian Macdonald, owner of Buccaneer Ltd. for kindly lending us the ROV and dropcam equipment.

Chart from Kevin Heath showing her mission area (over which her captain would have had some flexibility in the northerly limits). It shows where her mines were found (the numbers indicate the total detected per sweep). The UK Hydrographic Office wreck mark is shown by the green star - very close to where she had been laying mines.

Type UE boat plans

U 73 on training operations, a type UE 1 boat. Note the externally mounted bow torpedo tube (left)

U 73, stern tube (left) and deck gun visible

U 79 another type UE 1 boat (fourth from right) in Cherbourg dock, note again the external torpedo tube.

U 79 (2nd from left) in Cherbourg dock.

Sonar and video images of wreck

First sonar image of the wreck.

Curved single skinned hull section

Double skinned area of hull around the saddle tanks. Blanking plate or diaphragm from pressure hull would have been flush with outer hull.

Frame fixing outer hull to pressure hull.