'Hydra' (i) was a British special forces operation to land a three-man British and Yugoslav team of the Special Operations Executive from the sea into the Montenegrin area of Axis-occupied Yugoslavia (4 February/April 1942).

Two British Special Operations Executive agents and an officer of the former Royal Yugoslav air force were landed at Perazića Do, just to the north of Petrovac, from the British submarine Thorn. The three men were Major Terence Atherton, Sergeant Patrick O’Donovan (radio operator) and Lieutenant Radoje Nedeljković.

The operation failed completely in its attempt to develop contacts with Josip Broz Tito’s partisan forces, largely because the presence of the Yugoslav officer implied links with the Četnik royalist movement, and it is suggested that this caused Tito to suspect the British of being spies. With nothing gained, the British agents left Tito and soon after this disappeared, together with the large amount of gold and Italian money with which they had been entrusted.

The British liaison officer at Colonel Draza Mihailović's Četnik headquarters prompted Mihailović to order a formal inquiry into the fate of the Atherton mission, and a summary of the investigation’s results was later sent to the SOE office in Cairo: the investigation decided that the most probable culprit for the deaths of Atherton’s team members was a Četnik leader named Spasoje Dakić.