Congress passed a bill mandating them. Even though current thought is that they are outdated. Here is why. In WW ONE the battleship ruled. They had the long reach, being able to hit everything else before the other side could shoot back. Only another battleship could challenge them. In WW TWO the carriers became the ships with the long reach. They could easily hit the battleships before the battleships even got close. Nothing could really challenge a carrier except another carrier. HOWEVER, in DEC 41 when the USA entered the war, there were 18 fleet carriers between the USA and Japan. The big carriers. By DEC 42 ten of them, over half had been sunk. That was before over-the-horizon radars, satellites, cruise missiles, ICBMs, SLBMs, tactical nukes, etc. Today they no longer have the long reach. They can be hit by ANY ship with long range missiles, they can be hit by planes with standoff missiles, by land launched missiles, etc. They can be hit long before they are within range to shoot back. They are in the same position as the battleships were in WW TWO. They will not be all that useful and it will be subs that rule in the next major war.