Complex sentence: In April 1931 the Navy ordered 16 production aircraft to be designated the BM-1, another 16 were ordered in October 1931 as the BM-2, it was a variant with minor improvements.
Split into simpler sentences: In April 1931, the Navy ordered 16 production aircraft to be designated the BM-1. Another 16 were ordered in October 1931 as the BM-2, a variant with minor improvements.