Complex sentence: In 1949, the grades of W3 and W4 were created with Chief Warrant Officer now occupying W2, W3 and W4, then in 1953 the Warrant Officer Flight Program was created, which trained thousands of warrant officer pilots.
Split into simpler sentences: In 1949, the grades of W-3 and W-4 were created with Chief Warrant Officer now comprising the W-2, W-3, and W-4 grades. In 1953, the Warrant Officer Flight Program was created, which trained thousands of warrant officer pilots.