UB-8
... that when the German U-boat UB-8 was transferred to the Bulgarian Navy in May 1916, she became the first ever Bulgarian submarine?
... that when the <a href="./German_Empire" id="mwDuA" rel="mw:WikiLink" title="German Empire">German</a> <a href="./U-boat" id="mwDuE" rel="mw:WikiLink" title="U-boat">U-boat</a> <b id="mwDuI"><a about="#mwt47" data-mw='{"parts":[{"template":{"target":{"wt":"SMU","href":"./Template:SMU"},"params":{"1":{"wt":"UB-8"},"2":{"wt":""},"3":{"wt":"2"}},"i":0}}]}' href="./SM_UB-8" id="mwDuM" rel="mw:WikiLink" title="SM UB-8" typeof="mw:Transclusion"><i>UB-8</i></a></b> was transferred to the <a href="./Bulgarian_Navy" id="mwDuQ" rel="mw:WikiLink" title="Bulgarian Navy">Bulgarian Navy</a> in May 1916, she became the first ever <a href="./Bulgaria" id="mwDuU" rel="mw:WikiLink" title="Bulgaria">Bulgarian</a> <a href="./Submarine" id="mwDuY" rel="mw:WikiLink" title="Submarine">submarine</a>?