Strategy Page has the details:
The U.S. is sending another carrier task force to the Persian Gulf, and the ships are heading out four months early and will stay at sea for eight months instead of four. There are already two carrier task forces in the Gulf area, and for a short while there will be three when the third task force arrives in five months.
This is what the U.S. Navy describes as “surge capability” (getting the maximum number of ships to a war or hot sport in the shortest possible time). It’s a new policy, getting a workout here because of rising tensions in the Persian Gulf.
It all began eight years ago, after a massive surge for the invasion of Iraq. This caused several problems, one of them being a dip in morale. So the navy decided it had to keep ships at sea less often. That’s because the ships need more time in port for maintenance, and the more you keep the ships at sea (especially for more than four months at a time), the more sailors decide to leave the navy.
For the 2003 Iraq campaign the navy sent 72 percent of the combat fleet (221 of 306 warships, including seven of twelve carriers, 75 percent of the amphibious ships and 33 of 54 attack submarines). There were 600 navy (and marine) warplanes involved, and over 100,000 sailors and marines. But this was done in the midst of the navy’s usual (for several decades) routine of six month cruises followed by six months in port. The navy got so many ships and aircraft into the Iraqi campaign by skipping scheduled maintenance, keeping sailors at sea for very long periods and basically improvising. This meant that when the Iraq operation was over, the navy had more than half its ships out of action for months as maintenance for ships and rest for crews was caught up on.