The Germans used a small flat-bottomed motorised lighter or boat to move men and supplies around calmish waters - rivers, estuaries, the Baltic and Mediterranean. I-Lighters were particularly active around the Greek Islands.
I modelled these mostly using balsa wood. The original boats were around 15-18 m long so these are small models. They have a small one-barrelled automatic gun, an MG or 20mm cannon, on a mount near the bow.
I-LIGHTER Photo
This is the photo I used as a template .
These boats were involved in combat with British coastal craft in the Med.
I-Lighters were built all over Europe so they probably varied a bit. These plans are from a Dutch workshop. Note the association with Siebel.
Another take on an I-Lighter.
A wrecked I-Lighter found by divers off Croatia. This photo shows the stem.
Note that the bow is detached from the rest of the hull. Apparently I-Lighters could be disassembled for transport on trains.
You can read more on the Axis History Forum.
The last I-Lighters were used by the Finns on Lake Ladoga as gun boats with a 57mm gun fitted centrally .

Finnish Gunboat Underway
Again, these photos are derived from the Axis History Forum, which is a mine of expert opinion.
To show how small these craft were, here is one of my scratchbuilt models alongside an S-Boot. Both are 1:300 scale .