One of two operating Zumwalt Destroyer will need to have a main turbine engine replaced.
They completed acceptance trials in February, and the Navy accepted partial delivery of the ship in April.
It is taking over six months to replace the engine because a special rail system is needed to remove the engine and put in a new one. The system to enable engine replacement had not been designed when the Navy realized it needed one. Engineers had to finish the design and then install the system.
The Rolls-Royce MT30 engine costs $20-million.
The US will build a total of 3 Zumwalt destroyers for about $22.5 billion. The third one is being finished now and will start sea trials in 2019. On average the Zumwalt destroyers cost $7.5 billion.