President Vladimir Putin calls improving the Russian navy's combat capabilities a priority.The unfinished husks of three guided-missile frigates that have languished for three years at a Baltic shipyard show that is easier said than done.Earmarked for Russia's Black Sea Fleet, the frigates fell victim to sanctions imposed by Ukraine in 2014 after Russia annexed the Crimean peninsula, prompting Kiev to ban the sale of the Ukrainian-made engines needed to propel them.With Moscow unable to quickly build replacement engines for the Admiral Grigorovich-class frigates, construction stopped.