The tugboats came in the evening, carrying three dozen Russian sailors and pro-Russian militiamen who climbed aboard the Ternopil and told the crew to leave.

The captain of the Ternopil in the port of Sevastopol in Crimea lined up his crew of 91 men, thanked them for their service and told them that they were free to go.

Left with little choice, the sailors headed for dry land. On Friday, the mast of the Ternopil was flying the white and blue Russian navy flag. Their ship had become the enemy.

One of the crew, a 22-year-old sailor who preferred to remain anonymous, told AFP he was now stranded in Sevastopol with no job and a prospect of prosecution for desertion if he headed home to Ukraine.

"I had plans here, I wanted to stay in Crimea, to go to a university here," said the sailor, who had served for two years.

"Your fate can really be decided within hours," he said. "Our guys wept over the ship."

As the flags go down one by one on Ukraine's fleet in Crimea, Russian forces are laying siege to the few ships still refusing to stand down.

The command ship Slavutich was one of the last still flying Ukraine's flag on Friday, but it is increasingly isolated in a region that is strongly hostile to the new pro-Western government in Kiev.

Russia took control of the Ukrainian navy's headquarters in Sevastopol on Wednesday. Its commander, rear admiral Sergiy Gayduk, was detained and driven to Crimea's border with Ukraine.

Sporadic moments of defiance have continued. At a naval academy in Sevastopol on Thursday, a group of students refused to stand quietly as the Ukrainian flag was replaced by a Russian one.

During a speech by the commander of Russia's Black Sea fleet, Alexander Vitko, they defiantly sang the Ukrainian national anthem before heading back inside the school, videos from the scene showed.

Some are more sanguine about the situation, blaming the government in Kiev for failing to fight back.

It was every man for himself, said the sailor from the Ternopil: "I don't blame the Russians. We have been abandoned by the government."

For weeks, he said, the Ternopil received no direction from Kiev. The ship did not fire at the Russian intruders because the captain "did not want to start a war".

- Serve Russia? 'Why not?' -

The new pro-Russian authorities have meanwhile invited Ukrainian servicemen to switch allegiances.

Sevastopol's maverick mayor Sergiy Chaly on Thursday said they can either transfer to other Ukrainian bases, leave the military or enlist with Russian forces.

Dozens responded to the call on Friday to register their names at the headquarters of the pro-Russian militia in the outskirts of Sevastopol, surrounded with barbed wire and sandbags.

A deputy commander of the headquarters, sitting in a makeshift situation room with giant charts and lists of numbers of pro-Russia activists, declined to be interviewed, explaining that he "only talks to Russian television channels".

Not everyone is tempted by the offer of switching sides.

"If I join the Russian navy, they will send me somewhere as far from Ukraine as possible," said the sailor from the Ternopil, adding that his whole family is in Ukraine and he does not want to risk being tried for desertion when he returns. Instead, he hopes to emigrate to Europe.

But Maksim, a young man standing in line to register at the headquarters, said he now wanted to serve Russia.

"I served in Sevastopol, not in Ukraine," said Maksim, who is studying to be a military doctor. "Times change, but people stay the same."

Asked if he had a guilty conscience about making the switch, he said: "Yes".

"But I am a doctor first and a soldier second, and the Hippocratic oath is to the people, not any government."

For three months, Maksim was in Kiev, standing face-to-face as part of the riot police confronting anti-government protesters on Independence Square.

"We were hit, we were abused," he said. "Only a fool was not scared there.

"After that experience, I don't want to serve Kiev anymore," he said.