RAF Valley night rescues will halt from 15 November - 31 December
Helicopter search and rescue from RAF Valley on Anglesey will not operate overnight, to ensure day-time crews are up to strength.
The Ministry of Defence (MoD) said it was one of five bases to work 12 hours per day for about six weeks with cover provided by neighbouring stations.
RAF Valley will close overnight from 15 November until 31 December.
The MoD said the majority of call-outs take place in daylight, when rescue cover will carry on as normal.
The base is the home of C Flight 22 Squadron, which operates Sea King search and rescue helicopters and the Search and Rescue Training Unit, which operates Griffin helicopters.
An MoD spokesman said the changes were temporary and the number of search and rescue crews in the UK was being restored to 28 next year, after being cut to 26.
He said the planned closures would be managed in the same way as previous ad hoc closures to ensure that arrangements were in place for full cover of the UK at night-time.
The spokesman said the closures were to "ensure current levels of day-time coverage are maintained, safeguard crew safety, and preserve night-time response times".
Armed Forces Minister Bill Rammell said: "It is standard practice that, when a search and rescue station is not operating - which can happen for various reasons - the adjacent stations are able to respond.
"This process does, and will continue to, ensure that search and rescue cover is maintained throughout the UK 24 hours a day.
"I appreciate these changes have caused some concern but our search and rescue helicopter crews do a fantastic job and that will not change because of these temporary closures.
"Our crews provide a first-class service better than or comparable with anyone in the world, and that will continue."