Revealing mistake: The soldiers on the beach were armed with M-16 rifles. The movie period was 1962, during the Cuban Missile Crisis. The M-16 and M-16A1 were not manufactured until 1964.
Suggested correction: Just watched Matinee again after reading this. I saw M1 carbines, M1919A4 and M2.50 cal machine guns and M14 rifles. There are no M16 series weapons in this movie.