What does the acronym "M4" signify in the context of Navy weaponry?

The acronym "M4" in the context of Navy weaponry signifies "Modular Carbine." The M4 carbine is a highly adaptable rifle that was developed from the M16 rifle platform. It features a modular design, allowing for various accessories and components to be easily swapped out, such as optics, stocks, and grips, which enhances its versatility in different combat scenarios. This adaptability is a significant advantage for military operations, enabling personnel to customize their weapons according to mission requirements.

The term "modular" indicates not only the ability to modify the weapon but also refers to the standardized parts that can be used across different firearms in the same platform family, making maintenance and logistics more straightforward for the Navy and other branches of the military.