SEOGWIPO, Jeju Island (Yonhap) -- A large cassion structure to be used for building a breakwater off the Jeju naval base has been moved into position, the Navy said Saturday.

It said the 8,800-ton structure that is 38 meters long, 25 meters wide and stands 20 meters high has been placed on a floating dock and moved offshore near Gangjeong village.

It said the cassion will be the third such unit deployed off the planned naval base, located on the southern shores of Jeju Island.

Caisson is a watertight structure used to help underwater construction work in such fields as making the foundations of bridges, dams, seawalls and piers.

The Navy had temporarily halted construction of the naval base on March 27 at the request of the Jeju government to conduct simulations of the feasibility of using the base to dock large cruise ships.

It said by dropping the cassion, work to dredge the sea bottom, which started on April 7, will pick up pace. Dredging is necessary to make the water deeper for ships.

The naval base project launched in 2007 will create a modern military port capable of berthing 20 warships simultaneously and two 150,000-ton cruise ships. The base when completed in 2015 will give Seoul easy access to send naval vessels into the South Sea that is a key trade route for Korea.

The move, however, has run into stiff opposition from civic groups and environment activists who have engaged in numerous protests and filed legal action to halt construction.