It is funny how a project like this starts and then grows beyond anything you'd normally expect.
I believe it was Sagunt who showed a picture of his similar conversion a couple of years ago. His were designed to be steam-punk and had brass metals and red clothing. The pulseguns were trimmed and they looked the business. I took one look and thought 'I need to build some of those'... so I did.
I went a little further with the conversion by adding humps to the back... but I didn't trim the weapons down (I like the pulseguns

)... apart from that, I dug out a few spare Grymn and got converting.
At the time, I didn't even have squad sizes worked out. Then, at Salute, I found some little spider drones which I thought would make good comms troops and I bunched what converted troops I had into squads with a leader, a pair of special/heavy weapons and a comms robot... and 10 was about the right size. That meant I had to buy a few extra troops to fill out all of the squads I had... and that took the army to 6 squads. Then I thought... 'I may as well aim for a hundred troops with an additional command squad'...
...additional ideas came and went... tracked units that had walls that fold out and acted as moving barriers... Mystic Panda scouts... robots...
...other ideas stayed... a drone unit, a medical unit, a dog unit (with mini mawes) and a special unit which could include some OGrymn.
Of course, I had to find transport options and although I love the Old Crow range, I found the perfect little vehicles from Scotia Grendel's Kryomek range. They had a dimpled surface that made them look a lot like rocks (which suited the underground theme... even if they just stayed topside). I soon realised that I needed other vehicles to suit specific requiremenets... so the trawl went out and vehicles from Ground Zero Games and Fenris were drafted in. I have also succummed to Old Crow's charm and have a vehicle that will need to be converted for OGrymn use.
As all this was going on, I was trying to find a way of using some of my existing collection of miscellanea in a project of some sort. I had a couple of 1/35th scale VOTOMS troopers and a bunch of Warzone, Vulkan battlesuits that had remained homeless and this project called out to them. That is when I realised that things had really moved on from the small unit of Tunnel Fighters that I started with... so I had a re-think.
I put together a small army of Tyranids and got a picture in my mind of my Tunnel Fighters and their Clanker units charging into large tunnels and caverns to fight the nids.
... and that is where I am at now.
Once I have finished the special squad and its vehicle, the Clanker units and the transport for the medical unit... that will be the army finished.
When that happens... there will be much rejoicing

!