LOL, pretty cool.
in "Flags", only a 2 year old film, Clint Eastwood actually used the old school method, - mostly. So 600 extras, 17 Higgin's boats, and some LVT's, Shermans etc etc. The explosions were real (you felt lucky to have a tin hat when sand and pebbles were raining on yer head), and the Howitzers were actually loaded with a "projectile" (to get the punch right).