They sit in huge concrete  caissons that were prefabricated on land then dropped into trenches on the seabed.

他们坐在巨大的混凝土沉箱中，这些沉箱是在陆地上预制的，然后投入海床上的战壕中。

Peter Jackson's documentary, They Shall Not Grow Old, give us a rare insight into what is was like to fight in the trenches on the western front.

彼得 · 杰克逊的纪录片《他们不会变老》，给了我们罕见的见解，西部战壕的战斗是什么样的。

These immense structures, which are  as big as apartment blocks and weigh many thousands of tonnes each, had  to be manufactured in three separate locations before being dropped  into huge trenches on the seabed.

这些巨大的结构与公寓楼一样大，每个重达数千吨，必须在三个不同的地点制造，然后才能投入海床上的巨大沟槽中。