Final answer:
The National Guard and Reserve components supplement active duty units in worldwide deployments, playing significant roles in extended military engagements.
Step-by-step explanation:
The two units that supplement active duty units to create a major force in worldwide deployments to meet mission requirements are the National Guard and the Reserve components. Traditionally articulated by the slogan "One weekend a month, two weeks a year", these elements of the military have come to play much more significant roles. For instance, during the Iraq War, they comprised nearly 28 percent of the total US forces in Iraq and Afghanistan by the end of 2007. This increased reliance on the National Guard and Reserves reflects the changing nature of military deployments and the requirements of extended global engagements.