The history of the U.S. Armed Forces dates to 14 June 1775, with the creation of the Continental Army, even before the Declaration of Independence marked the establishment of the United States. The Continental Navy, established on 13 October 1775, and Continental Marines, established on 10 November 1775, were created in close succession by the Second Continental Congress in order to defend the new nation against the British Empire in the American Revolutionary War.
A major development in infantry tactics came with the increased use of trench warfare in the 19th and 20th centuries. This was mainly employed in World War I in the Gallipoli campaign, and the Western Front. Trench warfare often turned to a stalemate, only broken by a large loss of life, because, in order to attack an enemy entrenchment, soldiers had to run through an exposed 'no man's land' under heavy fire from their opposing entrenched enemy.
The IRT model underlying ASVAB scoring is the three-parameter logistic (3PL) model. The 3PL model represents the probability that an examinee at a given level of ability will respond correctly to an individual item with given characteristics. Specifically, the item characteristics represented in the 3PL model are difficulty, discrimination (i.e., how well the item discriminates among examinees of differing levels of ability), and guessing (i.e., the likelihood that a very low ability examinee would respond correctly simply by guessing).