how to get in those divisions ar?
i think it would be cool firing big guns
Speaking for Arty .... All gunners (& the mortarmen of old -- they're also in Arty) are mustered via mono-intake, although some of the ex-recruits are vocated as 7-tonner (or M113) drivers after BMT.
Likewise, you can get posted to the formation as officers (specializing after the 2nd-stage Service Term while in OCS), NCOs (specializing after BSLC in SISPEC) or technical vocationalists (after BMTC in Tekong), all three groups first undergoing requisite training at SOAY. How to get shortlisted? Generally speaking, your various course results, trainers' feedback, MAPAS scores, unit vacancies, etc. are all factors.
At the unit itself, you can get posted in as signallers, drivers, medics, storemen, clerks, et al. None are specifically Arty-trained although, for operational reasons, a lot of them end up inducted with the technical stuff & SOPs. Some of these outfield could later get to fire off an arty round or two, at least with the old SP mortars (mounted inside M113s) which used to go for live firing almost every week. The 155mm howitzers can only fire overseas, where every aspect of each mission is deliberately controlled anyway & so sometimes the order will come down asking if anyone wants to have a go at pulling the lanyard. First come, first served ....