The Admiralty purchased Jason when the Napoleonic Wars broke out. After the Treaty of Amiens, Britain had disarmed while France rearmed so on the resumption of war the Admiralty found itself short of vessels for convoy escort. Because of the urgency of the situation, the Admiralty purchased twenty such (three-masted) mercantile vessels; among them they took Jason into service with her original masts and yards even though she was under-canvassed and therefore slow, and without a cargo in her hold tended to roll; she became HMS Heron.