During December 2005, I was working on a model railway. It's something that happens to me occasionally - I make so much terrain that I decide I should make a model railway. I never finish them.
This time, something different happened. Sure, I never finished it. But I ended up with a 40K railway instead.
As a joke, my brother gave me a $15 toy train set he got from Toys'r'us. It's 'O' gauge, which looks right for 40K. He never though of it that way. I though of it that way right from the start.

The set included a Tank wagon, and an open wagon. Both where low on detail, but they used the same chassis as the carriages. The chassis were very nicely done, so it was just a question of detailing what sat on top.

The tanker was the simpler of the two. I just added a lot of rivets, and replaced the cat walk on top with one which was more in proportion with 40K (A miniature can stand up there now, the old catwalk was far to narrow) I also added a couple of outlet pipes, but you can't see them in this pic because they are on the other side. I replaced the petrol tanker markings with the livery of 'Pseudo Glop' liquid baby-food.

The open wagon was more involved. The existing version was not very good, so I decided to completely replace the body work with platicard. I used various plastruct girder shapes for detailing, and gave it a tread plate floor. It's big enough to hold a bout 8 minis.