this is a SUPER Pershing, one of only 2 made. One was sent to ETO for a "trial by fire"
it got into it with a Tiger close range, and killed it, they also say it killed a Panther at a distance
the tubes are recoil springs barrel, they also added armor in the field as they felt the tank needed more armor.
" The Super Pershing (aka T26E4-1) was equipped with a new long-barreled T15E1 90mm gun that was designed to out-perform the German high-velocity 88mm on the King Tiger. In testing, this new U.S. gun had successfully penetrated 8.5 inches of armor at 1,000 yards at 30 degrees. Even more remarkable, it had penetrated 13 inches of armor at 100 yards. The special 90mm ammunition had produced a muzzle velocity of 3,850 feet per second, or some 600 feet per second faster than the 88mm of the King Tiger. The new 90mm round also proved to have superior range and accuracy over the previous version."
from http://www.3ad.com/history/wwll/feature.pages/super.pershing.1.htm