According to the 1952 ordnance manual, the full name is “radially
expanded monobloc gun.” They had thinner barrels than your normal
built-up gun. Apparently, they made the tube from a single cylinder,
placed it under tremendous hydraulic pressure, “higher than that
developed during firing,” causing it to “expand radially.” After
removing the pressure, the outer molecular layers try to shrink to
normal size. The inner molecular layers, “subjected to greater force
and stretched proportionately more than the outer layers, cannot fully
return to their original size.” This tightened-up the molecular bonds
in the steel, making it a lot tougher than a built-up gun.

Making a gun becomes faster and cheaper plus it saves weight.
Supposedly, they could save 28,000 pounds on an 8″/55 gun & mount by
doing this. The big disadvantage, of course, was that there was no bore
lining. So, since you couldn’t replace the rifling, the whole barrel
had to be thrown out after it wore out the first time–much like
changing a machine-gun barrel. Gun mounts were redesigned to facilitate
easy changing, for example, “The barrel is connected to the housing by
means of a bayonet-type joint and locked by a key and key-bolt seated in
a keyway in the barrel. This design facilitates regunning the mount
without dismantling the breech mechanism or other parts.”

The gun factory history was unclear on how many of these were made but
the ordnance manual states that, owing to the inability to make really
large single forgings, only 5″/38 and 6″/47 guns had monobloc barrels.
The 8″/55 was actually a combination gun, i.e. having a partially
radially expanded outer barrel, to save weight, but an interior liner
that could be replaced.

3″, 40mm, and 20mm guns were made from single steel forgings without
radial expansion or built-up hoops. The pressures per square inch were
higher than on big guns but they just made them relatively thicker, the
weight ratio difference didn’t add up to much on small guns.

Timothy L. Francis
Historian
Naval Historical Center
email address: Francis.Timothy@nhc.navy.mil
voice: (202) 433-6802

> ———-
> From: Bill Riddle[SMTP:riddleb@fhu.disa.mil]
> Reply To: mahan@microworks.net
> Sent: Thursday, January 08, 1998 8:49 AM
> To: mahan@microworks.net
> Subject: Re[2]: USS NEW ORLEANSreplacement turret – solved
>
> Can some one educate this dumb soldier?
>
> What are “lightweight radially-expanded guns.”