A certain shed-based habitué of these parts (Hi Richard!) has suggested that it might be useful to share the basing conventions I use for 1/300th scale WW2 and Cold War units. So be it.
I've based my 1/300th scale vehicles since I moved over to playing rules where a single vehicle represents a platoon or more (Cold War Commander, TacWWII, Blitzkrieg Commander). I find bases help remind me that this is a unit, not just a single tank. In addition, regular-sized bases help me to store the models safely, particularly in magnetised drawers when the base has a layer of self-adhesive steel paper.
My basing conventions have evolved over the years but what follows is where we're at now. I'll give the dimensions in millimetres; width x depth.
Rifle platoons have four figures on a 30mm x 20mm base:
|Soviet WW2 rifle platoon
Some WW2 armies need tank riders. I've started making special bases for these. I cut out a 30mm square from an old business card. I then glue a few suitable figures along both edges and add 5mm strips in front of and behind the figures to make a 20mm wide channel into which a tank base will fit:
|Tank riders with T-34/76
Obviously when the riders dismount they are replaced by a normal infantry base.
Another recent tweak I've made is to mount my engineer units on 20mm x 30mm bases (i.e. portrait rather than landscape). This helps distinguish them from conventional infantry. I've also taken to adding flamethrower flames from painted clump foliage or barbed wire made from cotton thread and staples:
|Soviet assault engineers
Medium and heavy machine guns go on a 30mm x 20mm base with a single team depicted. Given that the gun crew are kneeling around the gun, it's easy to distinguish them from the riflemen:
|Cold War British sustained-fire MG
I put medium mortars (typically 81 or 82mm calibre weapons) and heavy (106-120mm) mortars on 30 x 30 bases.
I don't often represent lighter (50-60mm) mortars as separate units. I usually assume that effect of the British 2" mortar and the German 50mm is factored into the platoon's inherent firepower. However, the H&R US support weapons pack includes some nice 60mm mortar teams to I've started putting a few of them on 25mm x 25mm bases to make them easily distinguishable from their larger brethren:
|US 60mm and 81mm mortars
Artillery or anti-aircraft units, whether self-propelled, towed or man-handled, get 30mm x 30mm bases:
|US .50 cal AAHMG
I also use 30mm x 30mm bases for battalion HQ elements. A few suitable command figures make for a mini-diorama. I've recently started doing some of these with a space on the base where I can add an un-based vehicle if the HQ is for a motorised unit:
|Japanese battalion HQ
|The same HQ with staff car
Tanks, armoured personnel carriers, trucks the like generally go on a 20mm x 30mm base:
Tank HQ units are distinguished by appearing on a 30mm x 30mm square:
|Panther battalion HQ
However, I've recently started upping the depth where the model has a long gun that would otherwise overhang the base. These 3D printed IS-IIs are on 40mm deep bases, the HQ platoon being 30mm wide to distinguish it:
|IS-IIs on extra-deep bases
CWC and BKC distinguish between battalion and higher-level headquarter units. The latter, called CO units, get 40mm x 40mm bases; a great opportunity to try your hand at mini-diorama building:
|WW2 US CO base
The Commander series rules depict artillery observers and forward air controllers as separate units. I base these on 2 pence coins (25mm diameter), usually with a suitable vehicle and some dismounted observers:
|Artillery observer with 1 tonne Landrover
The same basing can be used to distinguish the Centurion OPRA from its Sabre troop equivalent:
Finally, a one-off. Years ago a wargaming forum had a painting challenge to produce a sniper unit. I decided to go tiny and did a 1/300th scale Frenchman with a .50cal. He went on a one penny (20mm diameter) coin:
|French sniper - he should probably
remove the brass badge from his beret!