It was the humidity, which was the reason why they were left open.
Later aluminium vents were deployed that cured this in the tropics.
Mark M Allen posted some shots of these, a while ago used to vent P-47N's on the Phillipines.
As for Iwo Jima P-51's ---
http://www.axis-and-allies-paintworks.c ... ic.php?384And just last week, sorry for Hi-jacking the thread.
IWO TO, Japan (Sept. 29, 2015) Nimitz-class aircraft carrier USS Ronald Reagan (CVN 76), while underway off the island of Iwo To, formerly known as Iwo Jima, pauses to honor the fallen service members of the Battle of Iwo Jima. This year marks the 70th anniversary of the end of World War II. Ronald Reagan's presence highlights how the relationship has grown between both countries who are committed to the peace, security and stability of the Indo-Asia-Pacific region. (U.S. Navy photo's by Mass Communication Specialist 2nd Class Paolo Bayas/Released)

