Complex sentence: Although it crashed, he learned a lot from its construction, and the Dornier-Zeppelin D.I was built in 1918, and although too late for operational service during the war was the first all metal monocoque aircraft to enter production.
Split into simpler sentences: Although it crashed, he learned a lot from its construction. The Dornier-Zeppelin D.I was built in 1918 and although too late for operational service during the war was the first all metal monocoque aircraft to enter production.