When does the firing delay time for the M904 mechanical nose fuze begin?

The firing delay time for the M904 mechanical nose fuze starts after the bomb has impacted. This timing is crucial because it ensures that the fuze operates correctly, activating at the right moment to detonate the explosive payload after it makes contact with the target. The design of the fuze includes mechanisms that delay the detonation until after the impact to enhance effectiveness and safety.

The other scenarios do not align with how the M904 is engineered to function. For instance, if the delay started upon release or deployment, there would be a risk of premature detonation, which would be unsafe, especially in the case of a live drop. Additionally, starting the delay upon arming would not accurately reflect the operational requirement that ensures detonation only occurs upon successful impact. Understanding the timing of such mechanisms is vital for effective munitions handling and safety protocols.