Kiev, Mar 13 (IANS/RIA Novosti): Three of the Ukrainian navy's killer dolphins who swam away from their handlers during training exercises, may have left in search for mates, an expert has said.

Only two of five military-trained dolphins returned to their base in the Crimean port of Sevastopol after a recent exercise, reported Ukrainian media reported earlier this month.

Ukraine's defence ministry denied the reports, while refusing to confirm the navy makes use of dolphins, despite the frequent appearance in Ukrainian media of photographs of dolphins with military equipment strapped to them.

"Control over dolphins was quite common in the 1980s," said Yury Plyachenko, a former Soviet naval anti-sabotage officer. "If a male dolphin saw a female dolphin during the mating season then he would immediately set off after her. But they came back in a week or so."

Dolphins were trained at Sevastopol for the Soviet Navy as far back as 1973. They were trained to find military equipment such as mines on the seabed, as well as attacking divers and even carrying explosives on their heads to plant on enemy ships.

After the breakup of the USSR and the division of the Black Sea Fleet into Ukrainian and Russian fleets, the dolphin training section and its specialists were handed over to the Ukrainian navy.

They were then used for civilian tasks such as working with disabled children, in order to keep the unit intact.