* Many Ukrainian troops ignore order to leave Crimea
* Russia annexed region after referendum
* Some military marriages fail to survive
By Alissa de Carbonnel
SEVASTOPOL, Crimea, April 8 (Reuters) - Ukrainian serviceman Ivan Marchenko's wife is filing for divorce over his decision to follow orders to withdraw from Russian-controlled Crimea. He is not alone.
Two of the servicemen sharing his berth on a train bound for Ukraine's heartland have also split with their wives who wanted them to stay in their home town of Sevastopol, now firmly in the grip of Russia's Black Sea Fleet after Moscow annexed the Crimean peninsula following a referendum last month.
Ukrainian military personnel face a stark choice: go back to the mainland or leave the service and try to make a new life in Russian uniform or as a civilian in Russian-controlled Crimea. Marchenko had a clear recollection of his conversation with his wife, whose name he didn't want to give.
"She told me: 'Go surrender. They (the Russians) pay more'," said the 27-year-old from Luhansk who served for ten years at a Ukrainian missile base near Sevastopol and is leaving his two-year-old son behind.
"Suddenly I'm an occupier. This is her city. She was born here. I mean I was born in Russia, in Magadan, but I grew up here and I am Ukrainian ... You only swear an oath once."
But the overwhelming majority of some 18,800 service personnel who the Ukrainian defence ministry says stuck out the month-long siege of their bases in Crimea are now ignoring orders - unswayed by purse-strapped Kiev's lacklustre offer to uproot their families and move them to the mainland.
Only about 4,300 will continue their service, Ukrainian defence ministry officials said.
Demoralised by Russia's swift takeover of their bases in reaction to the overthrow of Ukraine's pro-Moscow president after months of protests in Kiev, many more are instead trusting in President Vladimir Putin's pledge that they will be rewarded for swapping sides to join a Russian military newly revitalised by a sweeping modernisation.
Winning over their allegiance is a Russian propaganda coup but also a sign of the parlous state of Ukraine's army.
Its 180,000-strong military is no match for a Russian force that the government in Kiev and its Western supporters fear Putin could order into mainly Russian-speaking eastern Ukraine.
In moves Kiev described as part of a Russian-orchestrated plan to justify an invasion, pro-Moscow activists in eastern Ukraine have seized weapons in one city and declared a separatist republic in another.
Among the Ukrainian rank and file in Crimea, the split between those choosing to remain in the army and those choosing to leave the ranks is along geographical lines - highlighting the country's often muddled sense of national identity since independence in 1991.
In Crimea, under Russian rule for centuries and gifted to Ukraine by Kremlin leader Nikita Khrushchev in 1954 when Ukraine was part of the Soviet Union, ties with Russia have remained strong. Many people have relatives in Russia.
Out of a 308-strong battalion under his command in Kerch, Major Oleksy Nikiforov said only 59 were leaving Crimea with him. About 20 want to quit.
"You can talk about duty, you can talk about a military oath but you can't judge them in the current situation," he said.
"Many left because their whole life is here. Many because the political situation remains murky. Many want to join the Russian army because they got hooked on the promises Russia gave."
Stranded in no-man's land, some Ukrainians felt abandoned by what they saw as a lack of leadership by Kiev during and since the capture of their bases by better-equipped Russian forces, who urged them to defect.
"I was a young soldier when the country was just being born in the 1990s, when everyone had a lot of hope, but now Ukraine has existed 23 years and to dishonourably give up Crimea...," said Oleksy Khramov, a defence ministry spokesman, his voice trailing off.
"I want to come back, get a Russian passport and be a civilian. I don't have great hopes of Ukraine."
After friends, neighbours and in some cases wives voted in last month's plebiscite to approve Russia's takeover of Crimea, Ukrainian servicemen found themselves declared illegal by Crimea's new pro-Russian authorities but with nowhere to go.
As Kiev scrambled to organise their pullout, some have remained as part of negotiations to secure the return of some military hardware.
With emotions running high, a Ukrainian naval officer was shot dead in the dormitory where he lived with his family in a row with Russian soldier. It was the second Ukrainian death in what was largely a bloodless takeover.
The mood was glum among the young servicemen in baseball caps and civilian clothes taking the train out of Sevastopol.
"We are among the last to be deported," Ivan Samko, 21, wryly quipped. "We are northerners. Most of the others stayed."
In a small sign of resistance, some men hung a Ukrainian flag out of the window as the train pulled away. (Additional reporting by Pavel Polityuk; Editing by Giles Elgood)