Currently the Catapult's role is defined as either long range artillery, MRM carrier, or jump capable energy boat for the IS. But there are other roles that it can fulfill that the IS heavy mechs currently don't, and I want to present 2 ideas for them here as the Catapult D and Catapult E variants. I'd be interested to hear your thoughts.
Disclaimer: These variants are based off of my current grasp of the MWLL build system using CBT build rules as a basis for the designs. Using the Prime as an example, I figure that the Catapult has ~39.5 tons of pod space available to it. As such, the designs will utilize that tonnage as follows.
Catapult D - Short Range Missile Catapult
RA - DSRM6 - 7 tons
LA - DSRM6 - 7 tons
Torso - 2 ER Medium Beam Lasers - 4 tons
Torso - 2 Medium Pulse Lasers - 4 tons
4 Free Tons - 4 tons
6 Heat Sinks - 6 tons
MASC - 3.5 tons
Jump Jets - 4 tons
The Catapult D carries a hefty load out of 2 Dual SRM-6s with 4 free tons of ammunition to ensure that it can stay in the fight for a long time. At longer ranges it relies on 2 ER Medium Beam Lasers to reach out and touch the enemy, but these high heat weapons are really only there to provide it with some defense against aircraft and faster mechs that might think they can keep the catapult out of range. To supplement its SRMs in close range combat the Catapult D also carries a pair of Medium Pulse Lasers to provide accurate fire for finishing off damaged enemy components. A MASC system enable the Catapult D to reach speeds in excess of 90kph for short periods of time, allowing it to bring its SRMs to bear. 6 Heat sinks help to keep the Catapult D cool, but can quickly be overwhelmed if all of the lasers and SRMs are being fired continuously, especially if MASC is used too frequently or the Jump Jets have been used recently.
Catapult E - Self Reliant Artillery Catapult
RA - Arrow IV - 16 tons
LA - MRM30 - 11 tons
Torso - 2 Medium Beam Lasers - 4 tons
Torso - 2 ER Small Lasers - 1 ton
2 Free Tons - 2 tons
LAMS - 1.5 tons
Jump Jets - 4 tons
In order to combat the inability for the Catapult C to defend itself from enemy battlemechs that breached the firing line, the Catapult E removes one of the Arrow IV launchers and replaces it with an MRM-30 launcher giving it excellent firepower within the Arrow IV's minimum range and even overlapping it for a few hundred meters. To supplement the MRM-30 and reduce the machine's reliance on ammunition, a pair of Medium Beam Lasers are mounted in the nose along with a pair of ER Small Beam Lasers, proving the mech with a medium to short range punch to slice off damaged enemy components, while a LAMS protects the machine from return missile fire. As with all Catapult variants, the Jump Jets were retained, giving it good mobility into rough terrain and the ability to reach high ground where its artillery can be used to better effect. Paired up with a mech equipped with NARC beacons, the 'E' can inflict massive damage on a closing enemy with the Arrow IV and then finish it off with a tightly packed bloom of MRMs.