Russia has deliberately sunk three of its own ships to block Ukrainian navy vessels into a lake off the Black Sea, officers say, highlighting Moscow's determination to wear down the morale of Kiev's forces in Crimea. The Ochakov -- a Soviet-era warship decommissioned in 2011 and set to be sold for scrap -- was towed to the entrance to Lake Donuzlav on Crimea's western coast from the Russian base at Sevastopol on Thursday and blown up. It capsized and, along with two smaller Russian vessels, is now blocking the narrow gap between two spits of land, its hull beaten by rough Black Sea waves. Ukraine's navy has limited resources and suffered a major blow last week when its chief Denis Berezovsky switched allegiance to the pro-Russian Crimean authorities and a new chief was appointed. But officers at a base near where the Russians sank the ship have no doubt what the Russians were trying to do and insist they will not be shaken by the tactics. "It is blocked so we cannot get out," said Captain Viktor Shmyganovsky, second-in-command at the base in Novoozerne, one of the four biggest in Crimea. "If it wasn't blocked, we could have taken our ships to Odessa and it would stop them being seized by Russian forces. We would be more powerful in alliance with ships in Odessa." Ukraine's navy headquarters is in Sevastopol, where Russia's Black Sea Fleet was founded under Imperial Russia 230 years ago, but is currently barricaded by pro-Russian militants. Odessa, further round the coast into Ukraine and the country's largest port, offers a safer option amid the current military situation in Crimea, a semi-autonomous region of Ukraine where pro-Russian forces have seized control. - 'Loyal to Ukraine' - The Novoozerne base -- built by the Soviets in 1976 and dotted with decorative Cold War missiles and communications equipment -- flies the Ukrainian flag prominently and is protected by a handful of troops armed with Kalashnikovs. While Ukrainian officers would not disclose exactly how many men are based there, it is thought to be in the dozens. After the ships were blown up, the commander of Russia's Black Sea fleet, Admiral Alexander Vitko, came to the base trying to get them to switch sides, said Shmyganovsky. "He wanted us to swear for the Russian people. Members of the navy gave an honourable answer to the admiral -- Ukraine's soldiers will remain faithful to Ukraine's people," the small, neatly-dressed officer added. "A few military helicopters and planes were sent here (after the ships were sunk) and they were trying to break down our morale." Officers at the base declined to confirm how many Ukrainian ships were currently in Lake Donuzlav, while hinting at submarine capability. But Ukraine's navy is around a tenth of the size of Russia's and suffers from "inadequate finances", according to London-based military affairs think-tank the International Institute for Strategic Studies (IISS). Ukraine only has one, Soviet-built submarine which it is currently trying to restore to "service condition after over a decade of inactivity," it adds. Despite the odds stacking up against them, the Ukrainian navy is determined to stand its ground to the end in this storied naval territory, said Shmyganovsky. "From history, we know that those who cannot use political means resort to weapons instead. An admiral once said Sevastopol never gives up and we can say the same about other Ukrainian navy units," he added. "As you know, no Ukrainian navy units have put down their weapons except Admiral Berezovksy. None of the others swore for the Crimean or Russian people. We're staying loyal to the Ukrainian people."