The start of missile tube construction for U.S. and British submarines by General Dynamics Electric Boat Corp. has been authorized to begin by the U.S. Navy.

The authorization, worth $84 million, comes through a contract modification that funds a total of 17 of the tactical missile tubes -- 12 for the Royal Navy's Successor submarine; four for the U.S. Navy's Ohio Replacement submarine; and one for the Strategic Weapons System-Ashore test facility.

"This contract modification represents over five years of design and prototyping efforts between the U.S. and U.K. governments and their respective industry partners, and marks a key transition point for the joint CMC (Common Missile Compartment) effort," a statement from the U.S. Naval Sea Systems Command said.

"The OR (Ohio Replacement) program will provide the nation with its most survivable leg of the strategic deterrence triad. The program is harnessing 50-plus years of SSBN design and operational experience with the cost-control and production lessons of the Virginia-class attack submarine program, thereby providing the nation and its allies with an assured sea-based strategic deterrent at the best possible cost."

A joint U.S.-U.K. multi-year program for the nuclear submarines will eventually see a total of 241 missile tubes manufactured for the two navies.

Each Common Missile Container is about 45 feet tall and weighs about 50 tons. The U.S. Navy said the height is that of a four-story building.

Construction of the first Ohio Replacement submarine is expected to begin in 2021.