When I left Viet Nam in 1971, we flew out on a four engine plane. I can’t remember what it was.
About an hour out we lost an engine. The pilot came out and told us and asked if we wanted to go back to Saigon and get another plane.Nobody did.
I think I read somewhere that civilian airlines were often used to transport troops to and from RVN.Assuming that you weren't on a military aircraft it was probably a DC-8 or a 707...both of which had 4 engines.