Tracked and other motor vehicles made heavy artillery easier to move overland. A large river craft carrying artillery could also be difficult to conceal from counter-battery fire. Those changes reduced the attraction of concentrating heavy guns on river vessels. Minesweepers still had to keep the waterway usable for goods, so a task once assigned to small civilian boats became a central flotilla responsibility.
Notable Point · 34:24-35:31
Why minesweepers displaced heavy river artillery
Mobile land artillery reduced the need for heavy guns afloat, while mine clearance remained essential to keeping river freight moving.