Originally posted by Bronk
75 mm is just under 3". A 5" rocket is basically a 5" gun shell with a rocket motor.
Now what's easier to aim?
The 75mm cannon is more or less directly mounted under the pilot.
So where his nose is pointing thats where its going to hit.
I'd guess there is much less drop also.
Bronk
Diagram here System configuration here Excerpt from the website:Radar Gun Director: Each of VMB-613's aircraft was equipped with the AN/APG-13A radar gun director for the 75mm cannon. Commonly referred to as Falcon, it was developed by General Electric and operated on the S-band. It was designed to provide continuous range data and elevation corrections to the pilot's gun sight, allowing for the trajectory of each 15 pound shell at ranges of up to 5,000 yards. With this range, VMB-613's aircraft could effectively engage shipping targets while remaining outside of the range of light anti-aircraft fire. Designed for use against shipping targets, the AN/APG-13A was not effective against most land targets as rough terrain did not allow for good target discrimination at ranges in excess of 1,500 yards. The entire AN/APG-13A weighed approximately 105 pounds and consisted of the following:
Endfire Antenna - The most visible component, the endfire antenna, was mounted on the upper-nose of the aircraft on the axis of the 75mm cannon. It provided a sweep of 28 degrees of azimuth and elevation.
Indicator - The indicator was a radar scope that was operated by the copilot. Once the pilot had identified his target, the copilot would acquire it on the indicator at about 6,000 yards. As the run-to-target continued, the copilot would turn a crank on the side of the indicator unit to keep the range step on the radar scope lined up with the left hand side of the target echo. This action would turn a cam which would change the angle of the pilot's optical reflector sight, thereby providing continual range corrections to the gun sight. This eliminated the need for the pilot to estimate ranges and manually adjust the optical reflector sight.
Range Dial - The third component, the range dial, was located near the gun sight. Operated by the same action that adjusted the optical reflector sight, the range dial provided the pilot with the range to the target, enabling the pilot to determine when to commence firing and when to break off the attack in order to remain outside the range of light anti-aircraft fire.
Lighthouse Tube Receiver - The final component, the lighthouse tube receiver, was located under the copilot's seat. This device received the radar signal from the endfire antenna and fed the signal to the indicator.
A diagram of the AN/APG-13A radar gun director and photographs of the indicator, lighthouse tube receiver, and range dial is provided at the following link: AN/APG-13A Radar Gun Director
Annecdote from one of the Marines:"Anytime an aircraft returned from a mission, we needed to find out if the 75mm cannon had been used. If it had, we began a lengthy process to look over the entire aircraft. This was necessary as the firing of that cannon caused hydraulic leaks, and rivets in the airframe to shear-off. We used flashlights and crawled over every inch of the aircraft to locate leaks and damaged rivets so that they could be repaired before the next mission. Contributed by Michael Jacus Jr."
I encourage anyone that's interested in learning more about the aircraft and weapon system, check out the VMB-613 website at
http://www.vmb-613.com. If you click on the links to the months they were operational, you can read copies of the after-action reports. There are quite a few that reference using the 75mm cannon against gun emplacements, buildings, docks, and some small surface craft. Whether or not the 75mm could take out a tank is, IMHO, looking at the capability the wrong way. With an effective range of over 5 kilometers, you begin to be able to plink ships from outside ack range. Pretty nice capability if you ask me, even though puffy would still be an issue.
