Lancaster Mk II DS689 of No. 426 Squadron RCAF
This version had Hercules sleeve-valve engines with long flame- damped exhausts.
Reasons for the Lancaster B. Mark II’s Development
The Lancaster B. Mark II, equipped with Bristol Hercules XVI radial engines instead of the Rolls-Royce Merlin engines used in the Lancaster B. Mark I, was developed primarily due to concerns within the Air Ministry and RAF about potential production bottlenecks and vulnerabilities associated with relying solely on the Merlin engine.
Concerns about Merlin Engine Supply: The Merlin engine was the RAF’s primary power plant for various aircraft, including iconic fighters like the Spitfire and Hurricane, as well as bombers like the Halifax. This heavy reliance on a single engine type raised concerns about potential production shortages, especially with the United States entering the war and prioritizing its own re-armament needs.
Desire for Engine Diversity (Avoiding “All Eggs in One Basket”): The Air Ministry and RAF were uneasy about the vulnerability of depending solely on the Merlin. Should production be disrupted, either by enemy action or other unforeseen circumstances, the impact on Bomber Command’s capabilities would be significant. Developing a Lancaster variant with an alternative engine provided a crucial safety net.
Hercules as a Proven Alternative: The Bristol Hercules was a capable and available alternative to the Merlin. It had already been chosen as the power plant for the Halifax III bomber and was seen as a suitable engine for the Lancaster. This choice was also influenced by the desire to streamline engine production and maintenance within Bomber Command by utilizing a common engine type across different aircraft.
The initial success of the Hercules-powered Lancaster II, with its comparable performance to the Merlin-powered Lancaster I, validated the decision to pursue this variant. However, as the war progressed and Merlin production met demand, the need for the Lancaster II diminished. Additionally, the Hercules engine was deemed more crucial for the Halifax III, further reducing the priority of the Lancaster II.
Consequently, production of the Lancaster II was limited to 300 aircraft, after which Armstrong Whitworth, the company tasked with its production, transitioned to manufacturing the Merlin-powered Lancaster I and III.
The development of the Lancaster B. Mark II exemplifies the RAF’s pragmatic approach to aircraft development during World War II. The urgency of the situation demanded contingency planning and a willingness to explore alternative solutions to ensure the continued strength of Bomber Command.