Which WWII-era military procurement approach is considered the first true 'subscription service' model in military history, where manufacturers received ongoing payments for continuous weapon improvements?

Before modern professional armies, many militaries throughout history relied on various forms of enlistment and conscription. However, one revolutionary 'subscription model' in military history fundamentally changed how wars were fought and equipment was produced. This poll tests your knowledge of this pivotal shift in military procurement and technology development that still influences defense contracting today.

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The Cost-Plus Contract system, which guaranteed defense contractors profits above their costs, encouraging continuous production and innovation
The Lend-Lease program, where Allied nations 'subscribed' to American equipment supplies with deferred payment plans
The Five-Year Military Procurement Plan, where Soviet factories received predetermined funding regardless of production quality
The Spitfire Fund scheme, where British citizens 'subscribed' monthly donations to fund aircraft production