'Dive! Dive! Dive!' Is there any more evocative word in cinema, especially when repeated three times? We all know what comes next: periscope down, the sonar's ping, red light reminiscent of a photographer's dark room. The submariner's life is one of numbers, too: distance to target, torpedo tube one, distance from the ocean surface, ever-rising pressure levels.
If you think about it, depth charges and silent routine have been imprinted on our minds through only a handful of films. One of the best is The Enemy Below, starring Robert Mitchum and Curt Jurgens - all the regulation words and images are present and correct.
There's the man who cracks amid it all - who can't take it any more - he even tries to climb up the conning tower and open the hatch when they're under water. He's talked down by captain Jurgens: 'It is part of our work to die; we are not going to die. Do you believe me? Do - you - believe - me?' He does.
There's a great shot just before this point in the movie: the crews are absolutely still in the middle of the Atlantic waiting for the tiny noise that gives the other away. One US soldier is shown playing noughts and crosses while another is fishing over the side of the boat. Audaciously, the camera travels all the way down his line to focus on the sub, paralysed on the seabed. Here, the German crew is playing chess.
Incidentally, it's no coincidence sci-fi movies share much with submarine movies - that slim metal tube floats precariously in an alien environment. In the same way a U-boat's hull might give way - fatally - at any moment, so, 'The engines cannae take it, Cap'n.'
Geoff Dyer, whose Zona, about Tarkovsky's Stalker, is out now in paperback, itemises the distinctive tropes of the submarine movies in his memorable 1998 e-novel Paris Trance ('e', in those days, for ecstasy). Characters Luke and Alex pore through the pages of listings mag Pariscope for the best way to experience the city of (flickering) light, only to discover they're surrounded by Cassavetes films.
Made in 1957, The Enemy Below exemplifies what makes this genre so special: it's not the rakish fashions, the thrill of the chase or the heightened sense of claustrophobia - no, it's because these films consistently humanise the enemy. Like no other, the WWII sub flick is as interested in the other side as the heroes we're ostensibly backing. Could this be because the two sides are at different levels? This literally isn't a level playing field.
As captain Jack Hawkins tells his deputy after a gruelling chase in The Cruel Sea (1953) : 'Number One, this is quite a moment: we've never seen the enemy before... They don't look very different from us.'
Director Wolfgang Peterson extended the form for his groundbreaking 1981 TV series, Das Boot. Here we see the war entirely from the point of view of the German crew; as in The Enemy Below, a young Nazi ideologue onboard is humoured like a wilful child: wrongheaded, but what can you do? Here again is the captain portrayed as mythical seer, a man whose experience and guile will see his men home alive.
This is the best bit: the Second World War submarine film is visceral Battleships, a bloody mind game played out, usually by two mutually admiring leaders. As Jurgen Prochnow's captain declares at a crucial moment in Das Boot: 'Jetzt wird es psychologisch, meine Herren' - 'This is where it gets psychological, gentlemen.'
Submarine movies Operation Petticoat and The Bedford Incident screen on Film4 in the UK this afternoon from 1.20pm. Painting 'Torpedo... Los!' by Roy Lichtenstein can be seen in Tate Modern's retrospective of the US pop artist, which runs until 27 May.