US Airforce naval assault???

Here's a neat period picture. It's 1942 and US troops are hitting a foreign shore. However this is the Philippines and the troops are Army Airforce! This picture is from the excellent Osprey Publishing book: Fall of the Philippines.

What's truly weird is that the USAFFE had the 4th Marines sitting on Corregidor. These were fully trained infantry who would have been way more useful than USAAF personnel in an infantry battle. It is really odd that that marines, troops who were trained for this type of action, sat out this fight