The H/PJ-29 was an experimental naval gun project designed to test the feasibility of a fast rate of fire system. It featured four non-rotating barrels and fired 50mm shells with a delay of just 0.1 seconds between each barrel. The goal was to develop a naval gun that could rapidly engage threats with high precision and speed.

While initial tests demonstrated success in achieving the desired fire rate, a significant issue arose with barrel durability. After a few thousand shots, the barrels began to degrade due to the intense firing rate. This rapid wear and tear posed a serious problem, especially in sea trials, where the gun jammed during one test. The degraded barrel caused the shells to tumble inside, destroying the barrel from within and rendering the system unusable.

Despite its innovative design and potential, the H/PJ-29 was ultimately plagued by these durability issues, stalling its further development.