RX-77-3 Guncannon Heavy Custom – MechaBay

The RX-77-3 Guncannon Heavy Custom was a prototype artillery mobile suit developed by the Earth Federation Forces as an improved version of the RX-77-2 Guncannon.

The “R” in the model code meant it was a Federation model¹ and the “X” indicated that it was an experimental mobile suit. The “77” in the model code denoted that it was developed from the RX-77 Guncannon line, and the “3” suffix meant it was the third prototype in the line.

History

As development continued on the RGC-80 GM Cannon during the last weeks of the One Year War, Earth Federation Forces engineers continued tinkering with the design of the RX-77-2 Guncannon, refining it to be a standalone combat unit rather than simply a fire support mobile suit.

Following the development of the RGC-80 GM Cannon, a mass production variant of the RX-77-2 Guncannon, the Federation continued its development of medium-range support mobile suits. Based on the combat data of the RX-77-2, the Federation developed the RX-77-3 Guncannon Heavy Custom.

Although essentially little more than a retooled Guncannon, the Heavy Custom was considered a success, featuring better armour, improved 240 mm cannons, and a grenade rack on its left hip armour. Despite the RX-77-3’s improved performance, overall only a small number were produced due to the war’s end.

During the early part of the Gryps Conflict in U.C. 0087, at least one Guncannon Heavy Custom was known to have participated in the defence of the Earth Federation’s Jaburo base. In the manga Mobile Suit Zeta Gundam Define, Kai Shiden used a Guncannon Heavy Custom he found in a mobile suit hangar to escape from Jaburo base.

Units that continued to be deployed after the One Year War were eventually retrofitted with a panoramic cockpit monitor and other modern systems. The Heavy Custom remained in use as late as UC 0087.

Design

Compared to its predecessor, the RX-77-3 omitted the Core Block System and featured improved armour, reduced recoil, increased payload, rate of fire, and reloading speed. Its backpack output was also increased in an attempt to improve its mobility.

However, it was said that its weight was more than its basic design could support, hindering its mobility. In addition, while it was intended to be able to operate in both group and solo combat, its solo operation capability was said to be lacking.

The design philosophy emphasised enhanced firepower and defensive capabilities over the original Guncannon’s balanced approach. The removal of the Core Block System allowed for more efficient use of internal space and reduced mechanical complexity, contributing to improved reliability.

Armaments

The Guncannon Heavy Custom’s standard weapons were 240 mm cannons for ranged artillery support and vulcan guns for close defence, with optional beam weaponry for precision engagements.

60 mm vulcan guns

A pair of shell-firing armament built into the head. Low offensive power, only used to restrict enemy movement, and lay down a wall of suppressive fire due to their rapid-fire capability. These rapid-fire weapons were primarily effective against lightly armoured targets and served as defensive weapons against incoming missiles and aircraft.

240 mm cannons

Like the original Guncannon, the Guncannon Heavy Custom’s main weapon was a pair of shoulder-mounted 240 mm cannons. However, the Guncannon Heavy Custom’s cannons had better offensive power due to a higher rate of fire and a better ammunition feed system. The recoil during firing had also been reduced, and although this issue was not completely eliminated, it did not cause much problem during practical use.

These improvements made the Heavy Custom significantly more effective in sustained artillery bombardments compared to its predecessor.

Beam cannon

In order to solve the recoil problem completely, some test units had their cannons replaced with a single beam cannon for trial purposes. Instead of the shoulder mounted cannons, the Guncannon Heavy Custom could be fitted with the same beam cannon and targeting unit as the RX-77-4 Guncannon II.

This configuration provided more precise long-range engagement capabilities without the ammunition limitations of conventional shells.

Beam rifle

The Guncannon Heavy Custom could use the same beam rifle as the RX-77-2 Guncannon. This particular beam rifle was specialised for sniping. Compared to the beam rifle used by the RX-78-2 Gundam, it was harder to use but had higher accuracy and longer range. It was said to have a range of around 30 km.

RGM-79 beam rifle

The same weapon as used by RMS-179 GM II, it had a power rating of 1.9 MW and was powered by a built-in energy CAP system. This beam rifle was used by the Guncannon Heavy Customs stationed in Jaburo during the Gryps Conflict.

Hand grenades

The Guncannon Heavy Custom had an unknown number of hand grenades stored in a rack on its left side armour. Various types of hand grenades could be stored, providing the mobile suit with close-range explosive options for bunker-busting and anti-personnel operations.

Known pilots

Kai Shiden - used a unit found at Jaburo during the Gryps Conflict

Variants

Several test units would later be converted into RX-77-4 Guncannon II. A Type D variant with a different weapons loadout, the RX-77-3D Guncannon Heavy Type D, was also created with improved mobility features and additional equipment options.

Behind the scenes

Okawara Kunio was the original mechanical designer for the MSV version, whilst Mika Akitaka designed the Silver Phantom version.

The Heavy Custom was introduced as part of the Mobile Suit Variation line and later appeared in various Gundam media, most notably in Mobile Suit Zeta Gundam Define.

Appearances

Mobile Suit Zeta Gundam
Mobile Suit Gundam: Silver Phantom
Mobile Suit Zeta Gundam Define

External links

RX-77-3 Guncannon Heavy Custom on MAHQ
RX-77-3 Guncannon Heavy Custom on the Gundam Wiki

Federation in Japanese is renpou, hence the use of “R”. ↩