Somebody could write a book about all of the movies Charlton Heston made in the 1970's. Seventeen wildly varying movies, everything from a PLANET OF THE APES sequel to THE OMEGA MAN and SOYLENT GREEN, a western, some historical actioners and a number of disaster movies including this submarine crew in peril flick GRAY LADY DOWN. The film opens with longtime sub captain Heston bringing his ship into port for the last time. Normally you would stay underwater until you got there, but Heston is happy and tells 'em to go topside. Almost immediately they're hit by a gigantic freighter. With a breached hull, the sub sinks down 1450 feet and comes to rest on the edge of huge drop off. With only a limited amount of air and supplies, the crew needs to be rescued as quickly as possible, but during the wreck some heavy rocks landed on the exit door, so that means the Navy has to use an experimental mini sub (piloted by David Carradine) to clear the way for the Deep Submergence Rescue Vehicle.
For a one time watch GLD is a good movie. The special effects are dated, but not distractingly so, the pace is quick enough and the story is pretty good. If you watch it you'll be entertained, if you don't watch it you're really not missing anything. Personally I prefer my 70's disaster flicks to be bigger and have normal people in danger. Something like EARTHQUAKE or THE TOWERING INFERNO.