The first ships used triple-expansion engines, M18 received four-cylinder semi-diesels, and later vessels are associated with Campbell paraffin engines. Published horsepower figures and machinery assignments should be treated as guides because the sources disagree or remain vague. Those gaps show how poorly small wartime craft can be documented compared with battleships. The machinery choices also lead into the importance of power density for naval aircraft and small boats.
Notable Point · 11:11-13:08
Propulsion shortages and uncertain monitor records
The M15 class's mixture of steam, semi-diesel, and paraffin machinery exposes both emergency-production compromises and gaps in the surviving technical record.