The Sikorsky S-61N is a twin-engine medium utility helicopter with a sealed hull for amphibious operations
that can accommodate a basic crew of two and up to 26 passengers. The Sikorsky S-61N is
built by the American manufacturer Sikorsky Aircraft Corporation and based on the military
Sikorsky SH-3A/S61B Sea King series originally developed in the late 1950s for all-weather operations. The Sikorsky S-61B
prototype flew on 11 March 1959 and the type entered service with the U.S. Navy as the SH-3A Sea King in 1962.
The Sikorsky S-61N and its non-amphibious configurated variant Sikorsky S-61L are based on and essentially a commercial equivalent of
the military S-61B incorporating a number of changes, including a longer fuselage. The Sikorsky S-61L was flown for the first time on 6 December
1960 and received its FAA Type Approval on 2 November 1961. The S-61L entered production the same year. The Sikorsky S-61N with sealed hull and
stabilising SH-3's floats flew first on 7 August 1962. The S-61N version is optimized for overwater operations, particularly
oil rig support. The initial production S-61s were fitted with two 1250shp General Electric CT58-110-1 turboshafts. Both the S-61L and S-61N were
subsequently updated to Mk II standard with more powerful CT58-140 engines giving better hot and high performance and
other improvements and detail refinements. Production of the commercial Sikorsky S-61s ended in 1979
with over 1300 built. The ICAO Aircraft Type Designator for the S-61N helicopters is S61.
On 30 March 1976, the 1976-built Sikorsky S-61N s/n 61765 was registered G-BDOC in the UK with Bristow Helicopters Limited at Redhill Aerodrome.
The aircraft was christened 'Tolquhoun'. On 3 April 1985, the G-BDOC was stationed at Sumburgh at the Shetland Islands and operated and maintained
on behalf of the UKMCA UK Maritime and Coastguard Agency on the HM Coastguard services at MRCC Sumburgh as the primary SAR helicopter.
On 1 October 2007, the SAR unit at Sumburgh moved from Bristow to CHC Scotia and the G-BDOC departed Sumburgh for Aberdeen.
After undergoing scheduled maintenance in Aberdeen, Bristow Helicopters directed the aircraft to Den Helder Airport in the Netherlands.
Sikorsky S-61N MkII G-BDOC "Coastguard Oscar Charlie" arrived at Den Helder-De Kooy on 22 October 2007.
At Den Helder, Sikorsky G-BDOC was operated by Bristow in company with Sikorsky S-61N MkII G-BIMU on their offshore SAR contract.
On 15 December 2009, the G-BDOC returned to the UK and was replaced on the SAR contract by S-61N G-BPWB. Sikorsky S-61N MkII
G-BDOC was sold to Carson Helicopters in the USA and registration G-BDOC was cancelled on 7 September 2010. The same day, the Sikorsky was registered N426GE with
Carson Helicopters Inc. On 9 November 2011, the N426GE was registered with US Department of State, Patrick AFB, Florida, and on 18 January 2012, re-registered
N765AW. In November 2015, the helicopter was offered for sale by GSA Auction, a Federal Agency that sells property that the Federal Government has purchased, used,
and no longer needs. On 7 January 2016, the airframe was sold to an unknown owner in Wood Dale, Illinois. On 26 September 2016, the N765AW was registered with Ep
Aviation, Palm Bay, Florida. After the CofA expired, the Sikorsky S-61N MkII was stored and offered for sale. On 12 February 2020, the N7675AW was seen stored
by Clayton International Inc. at Peachtree City, Georgia. On 12 June 2020, the N765AW was registered with Clayton International. On 13 June 2022, Sikorsky S-61N MkII
N765AW was registered with Croman Corp., White City, Oregon.
On 19 September 2009, Sikorsky S-61N MkII G-BDOC 'Tolquhoun' was seen during the Heldair
Show Maritiem 2009 at Den Helder Airport / Maritiem Vliegkamp De Kooy.