Radar Men of the Moon is the second of the Rocketman serials and because it's in public domain, I've owned a copy forever. It's one of the very first movies I ever picked up on VHS.
It's probably in fact the first serial I ever owned aside possibly from Flash Gordon Conquers the Universe. This one features the Rocketman again, but he's dubbed "Commando Cody" this time out.
George Wallace leads the cast this time with Roy Barcroft as the Moon leader Retik who leads an invasion of Earth and Clayton Moore (the Lone Ranger no less) as Graber the lead henchman who helps the Moon Men with their schemes.
This one offers up the Rocketman again with some of the same stunts repeated and it adds a rocketship which gets Commando Cody and his team to the Moon twice during the run of the serial.
There's much running around, lots of great fights, and some dandy high-pitched acting from all involved. The serial gets a little ragged with some time-wasting moves now and again and I was surprised to find out that Moon Men need to rob banks and whatnot to fund their invasions of Earth.
Lots of classic serial moments are in this one. Getting a copy is dead easy as practically every collection of serials offers this one. The atomic ray gun is a fun toy and while you never really feel these guys from the Moon really are a threat the battle is a hoot.
UPDATE: This continues to be among my favorite serials. Not because it's that good, it's weak in many respects, but the pacing and the sheer bravado of the story it tells is no-holds-barred. No doubt I have a lot of nostalgia for it, but also it's just amazing that we have a story of alien invasion, a trip to the Moon, sundry small-time hoodlums, and an awesome rocket pack in one yarn. The word for this one is "rip-snorter".