Complex sentence: Production models, built in unknown quantity, were originally designated TD2D-1, however the Navy changed its designation system in 1946 and the XTD2D-1 and TD2D-1 were redesignated as XKDD-1 and KDD-1, respectively.
Split into simpler sentences: Production models, built in unknown quantity, were designated TD2D-1. The Navy changed its designation system in 1946 and the XTD2D-1 and TD2D-1 were redesignated as XKDD-1 and KDD-1, respectively.