During WWII, the Korean War, and even into the Vietnam era
the U. S. Signal Corps designated many of their telegraph (Morse code) keys with a "J-" and a number. The real workhorse key during those years was the J-37.
There are many more glamorous wartime keys around, but the keys that carried the bulk of the action were the J-37 keys.
The J-37 key is unusual because, with the addition of different bases and connections, it became part of other more special purpose keys.
The J-37 radio telegraph key; no shorting bar, flat spring, plastic frame. J-37 keys are small, lightweight, and rugged.
Weight reductions come in the form of a frame made of black phenolic resin.
The electrical connections are easily accessed metal straps fastened directly to the binding posts,
with the leaf spring serving as one of the connections.
Their size and construction make them an excellent choice for a backup or portable key.
The J-37 is a very smooth key. The leaf spring of the J-37 is softer on the fist. Many people think
that leaf springs used on the J-37's, have better compression characteristics than coil springs
which are used on keys like the J-38 and other triumph style hand keys, and because of that
prefer the J-37.
The J-37 key is versatile.
With the addition of different bases and connections, it can serve on the desktop, mobile, or even leg mount (J-45).
A nice J-37 key will be very serviceable for reasonable investment and last for many years.
One modification to consider is adding a Navy knob. This may make a good key even better.