Westland Whirlwind Helicopter

The patrol in 'Merdeka' is inserted into the jungle by Westland Whirlwind helicopters.  The Westland Whirlwind helicopter was a British licence-built version of the U.S. Sikorsky S-55/H-19 Chickasaw.  400 were built, of which 100 were sold to overseas  customers. 

According to Wikipedia 69 still survive and when researching the book I visited Whirlwind HAR.9 XL875 at Scone Airfield, Perth, Scotland.

The RAF HAR Mk.4 version was modified for use in the tropics and was used in Malaya.