Im thinking of making a prompt revolving around the SS Explorer, a 6 man diving bell that used muscle power to move it forward and was launched in 1866. However its inventor was prevented from making it earlier by sickness and the Navy wanting the Alligator which originally had oars and sank heading to fight the Merrimack in a storm (Not its fault here).
However Explorer worked, with a pressurized hull and if not for pearl fishing choices would've turned a profit before the men went under with Possible "Bends" as they were at the right depths for that killing its inventor and crew.
is there a way to discover this phenomenon before the 1870's?