I love soldiers on layouts! Especially 1:43-1:50 scale soldiers on an O or 1:64 troops on an S gauge.
Soldiers, SWAT, police, government, borders, etc... are one of my favorite parts of my layout. In terms of modern O scale, there's the MTH set which has 6 soldiers, the K-line set of 9 and the nearly identical O-line Repro set of 9. Same goes for non-action posed SWAT figures(regarding K-line and OLR).
I have a package of these, in winter clothes, and a single American sitting at home waiting for me...
https://www.ebay.com/itm/CORGI...9:g:RWkAAOSw7Zdd5TD8
Corgi :Forward March: 1:50 scale. Spun Die-Cast soldiers. They made 6 sets of these in 1:50 scale. American, German, and British. Discontinued in 2006, I believe, but Russian and Canadian sets were in the works. They also had the 1:50 scale 'Skirmish' series which had 3 soldiers and a vehicle.
Finally, Corgi made a couple 6 WW2 "Forward March" dioramas, which I discovered and got my hands on one right before Christmas. They came with 3 soldiers, a vehicle, and the diorama depicting a battle from WW2. The dioramas could be posed together. Picture of the one that I have is below.
Box is to the right
Unboxed Diorama, 3 American Soldiers and a Sherman. Not yet on my layout. The 1:50 scale soldiers don't look out of place by the K-line or OLR and look fine posed by other modern o-scale figures. The MTH soldiers are a bit smaller so they also call for strategic placement.
On the left side of the tracks 2 Germans patrol the border with their AA gun equipped half-track(those are fromthe 'Skirmish' set. On the right side are metal American soldiers on patrol. They're what I'd call a tall S-scale(a bit over an inch) strategically placed away from the rest of the army due to the size difference. That said, soldiers of that size are so difficult to come buy I had to pick them up plus they weren't too expensive.
Finally, Corgi also made 6 packs of true S-Scale soldiers. They came in a blue blister pack. They're neat but almost too short to pose near plasticville figures.
Solido made some o-scale military vehicles that included 2 soldiers in non-action poses but I never pulled the trigger on buying any. When it comes to something other than 1:43rd scale and Solido, it's hit or miss for me.
I never bought a Tamiya set of soldiers but did buy a 1:48 scale battleground accessory set(didn't realize it was a model kit) with some brick walls, sand bags, etc... This weekend, I got frustrated with a stuck screw so I decided to try my hand at painting some dollies, boxes/freight, parts of a Lionel watch tower, touching up a few plasticville figures, and then painting one from scratch- I didn't do too bad! Gave me enough confidence that the next time I head to my LHS I'm picking up a Tamiya kit of soldiers.