Which advertising method was MOST commonly used by military equipment manufacturers during World War II to promote their products to government procurement officials?

Throughout history, military equipment manufacturers and suppliers have employed various advertising strategies to promote their products to governments and armed forces. From ancient weapon forges to modern defense contractors, product advertising has evolved dramatically while maintaining certain core principles. This trivia question explores how military equipment was historically advertised and promoted before the digital age.

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Technical demonstrations at military expositions and trade shows
Radio advertisements targeting the general public to build political support
Extensive billboard campaigns near government buildings
Celebrity endorsements from popular civilian entertainers