They searched for 81 years and found it at a depth of 203 meters in the Aegean

This is the HMS TRIUMPH, whose traces disappeared 81 years ago in the Aegean. Since then, the submarine had been the subject of research by various teams from England, Malta and Russia who from time to time visited Greece with the aim of finding the lost submarine, but to no avail.

The mystery was solved by researcher Kostas Thoktaridis and his team. The story of the submarine is multi-dimensional and unique in naval annals as it is inextricably linked to the Greek national resistance and the secret services of the era that operated during the occupation.
TRIUMPH began her intense operational action in May 1939. In total she carried out 20 war patrols. It first appeared in the Aegean at the end of March 1941 with the aim of reconnaissance of the coasts of the Dodecanese and the disembarkation of officers by canoe on the shores. Significant successes followed as she sank several enemy ships including the Italian submarine SALPA.

The sub undertook difficult and dangerous missions with landing agents of the British SOE and MI9 organizations and rescuing trapped military personnel who had to escape to Alexandria, Egypt.
Traces of the Triumph disappear and on 23 January 1942 the British Admiralty reports in a naval signal that the submarine Triumph must be considered lost after a patrol in the Aegean.

Over the years there have been many conspiracy theories about the circumstances of the submarine's disappearance. The possible causes were many: from a floating mine in Milos, from an impact on dry land, from an arrest by the German forces in collaboration with Italian agents, from an accident, from a deep dive, from an impact with a mine in the known minefields off Antiparos, even that it is a story a myth to cover up intelligence inadequacies ... everything was within the possibilities, thus greatly increasing the size of the field of investigation to identify him.

Eighty one years later, the team of Kostas Thoktaridis discovers the lost submarine in the Aegean at a depth of 203 meters. According to K. Thoktaridis, the submarine is resting on the bottom of the open sea with an 8 degree right inclination, tens of kilometers away from the coasts. Her lowered periscopes and closed manholes testify that the TRIUMPH was in a deep dive during the last dramatic moments. The depth and direction rudders are in line so it was at a constant depth.
On its turret, the wooden rudder, compass and four-inch cannon can be seen which is slightly raised. The facing manholes in the gun bay leading to the interior of the hull are also closed. On the forward side of the bridge the door leading to the gun has been opened... All hatches are closed. Throughout the hull of the submarine the plates and connections are with riveted sheets.

The final cause of the sinking appears to have been a large explosion in the bow of the submarine, which then drove H.M.S. TRIUMPH at a depth of 203 meters (666 feet).
But what caused this explosion that sank one of the largest submarines of that time?