Hall XPTBH
... that the Hall XPTBH, a patrol torpedo bomber, was the only aircraft that ever received three mission designation letters in the U.S. Navy's aircraft designation system?
... that the <b id="mwAU4"><a href="./Hall_XPTBH" id="mwAU8" rel="mw:WikiLink" title="Hall XPTBH">Hall XPTBH</a></b>, a <a href="./Maritime_patrol_aircraft" id="mwAVA" rel="mw:WikiLink" title="Maritime patrol aircraft">patrol</a> <a href="./Torpedo_bomber" id="mwAVE" rel="mw:WikiLink" title="Torpedo bomber">torpedo bomber</a>, was the only aircraft that ever received three mission designation letters in the <a href="./United_States_Navy" id="mwAVI" rel="mw:WikiLink" title="United States Navy">U.S. Navy</a>'s <a href="./1922_United_States_Navy_aircraft_designation_system" id="mwAVM" rel="mw:WikiLink" title="1922 United States Navy aircraft designation system">aircraft designation system</a>?