A deal worth more than £100m, will see the Coastguard replace its fleet of seven helicopters with faster aircraft.
The new helicopters will operate from July 2007
The Maritime and Coastguard Agency will lease seven aircraft from a Canadian operator to provide coverage for the south coast of England and in Scotland.
The new aircraft will replace the seven helicopters operating from Scotland's Stornoway and Sumburgh Lee-on Solent, Hants, and Portland in Dorset.
The current Search and Rescue (SAR) fleet of S61Ns was designed in 1961.
The MCA said it has signed a five-year interim contract with Canadian helicopter operator CHC Scotia to lease four Sikorsky S92 helicopters and three Agusta Bell AB139s to provide coverage from July 2007 to 2012.
Two S92s will be based at Stornoway, another two at Sumburgh, while two AB139s will be based at Lee-on Solent and one at Portland.
John Astbury, chief coastguard and director of maritime operations, said the deal was worth more than £100m.
He added: "The new aircraft are faster and will have greater endurance and this demonstrates the UK Government's commitment to search and rescue in the UK.
"The S61N, as the name indicates, were born in 1961, so they are approaching more than 40 years old at the moment. Although they are efficient aircraft they are very old machines.
"At some point there has to be a departure from existing aircraft otherwise we will end up with machines flying around on search and rescue that will be 60 or 70 years old and I think that it's entirely unacceptable to members of the public."
Angus MacNeil, Scottish National Party MP for Na h-Eileanan An Iar (The Western Isles), raised concerns about the suitability of the Sikorsky.
He said: "It is a shame that there was no opportunity for parliament to scrutinise the effectiveness and the suitability of the new S92 helicopters as this has a direct effect on safety and wellbeing around our coasts."