Mature weapons often work first when war begins

Why do old weapons reappear in later wars, and how long does it take new weapons to work reliably?

Mature systems have accumulated testing and service knowledge; newly introduced weapons are less likely to work smoothly at first.

Veteran tanks and old torpedoes illustrate a general procurement problem when weapons enter combat. A mature system has accumulated test firings, maintenance experience, manufacturing corrections, and operator knowledge. A newly introduced weapon may offer better theoretical performance but has had fewer opportunities for hidden defects to appear. The depth and realism of prewar testing therefore govern how quickly new equipment becomes trustworthy, which explains why older weapons can remain the first reliable choice in a new war.