A "generic" wooden Pontoon Bridge for your troops to assault (or even flee) across water obstacles.
This is a multi piece .stl 3D rendering is scaled for 15mm and comes ready to print, and only requires painting (and possibly some gluing) to make it tabletop ready.
The download includes a single pontoon boat and 2 "decks" that can be used as needed to create bridges of varying lengths. Also included are three pieces that can be printed to create a simple wooden bridge. Two heights are offered depending on the "river banks" of your own terrain, though it is recommended that you glue the pieces together if you do this.
Based initially on Felician Myrbach's watercolour of a pontoon bridge breaking up during the Battle of Aspern-Essling (see here) but since I also wanted it to be a "generic" pontoon bridge it was further inspired from photographs held in the US Library of Congress. (see LC-DIG-ppmsca-33385, LC-DIG-ppmsca-34932 and LC-DIG-ppmsca-33352) for representative inspiration.
For other scales, I suggest the following, though you may prefer to experiment to ensure the model "looks right" on your tabletop: