There have been a number of times since the USMC took its AV-8Bs to sea aboard the LHAs & LHDs that they have needed some sort of FJ air cover and a CVN was nowhere near... Liberia 1990 for example*. All the CVNs were scrambling to the opposite side of Africa, leaving the MEU all by itself... and a call came in for their help.
The rebels had control of and were flying some fighter aircraft, and the USMC really didn't want to provide cover for the helos evacuating embassy personnel & civilians with just their Sea Cobras... it was a good thing they had some Harriers along.
In a few years the Harriers will be all gone, and if Dave-B is canceled there will be NO "fast air", stealthy or not, for the Marines to deploy
without a CVN... and with the reduction in numbers of the CVN force over the previous CVN/CV force, the liklihood of being tasked with a low-level (but still with air threats) mission and being told "sorry, no CVN available, do it by yourself" is increasing steadily.
*
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In 1990, Liberia exploded into a bloody civil war that continues to this day. During this time, USMC forces have engaged in three incursions into Liberia, the last one occurring in May 1996. Despite these recent actions, most military officers remain largely unaware of the Liberian war, its causes, or the historical ‘special relationship’ existing between the United States and Liberia.
All 3 times, no CVN was provided... the USMC made do with cover from AV-8Bs on flat-topped amphibs.