Oliver Wood: Water, Water, and More Water.

From ICG Magazine, Watership Down by Pauline Rogers (May 2000)

Compressed Nitrogen:
"The set piece was hung over an area with a drain," says Wood. "We would pour water into the set-- and I mean pour-- and shoot. The water would then be drained away and we would go again. To protect the fronts of the lenses, we used Nitrogen air blowers like the ones we used on Face/Off. These blowers were so effective, we could literally walk the cameras through a wall of water-- moving with the actors, to get the intensity of the action."

Mag change!
Off the island of Malta, production constructed a 100 percent scale duplicate of a U-boat, weighing in at some 600 tons. Additionally, two full sized, tops of subs were floated in giant water tanks. "These were two 220-foot long 'subs,' surrounded by gigantic towers that poured salt water rain on the action all the time," confirms Wood. ... "The cameras had to be completely covered in plastic. That meant it took about 15 minutes to change the 400-foot mags. Although well-protected, the cameras kept breaking down from the abuse."

Peter Donan on the miniatures:
"When doing underwater shooting, the miniatures were shot using available light, as we were working about 15 to 20 feet underwater," describes Donan. "In order to control the quality of the light on these boats, we had silks made that were almost 180-feet long by 150-feet wide. They were created out of sailboat spinnaker cloth. We used this material because of its superior resistance to UV [light] and saltwater... At one point, we even had to paint the tank's bottom black to cut down on bounce reflection. That way, we could get additional shape from the hull and prevent it from looking too lit."