History

This unit joined the shack on October 3, 2023, courtesy of an eBay find.

Above: My favorite straight key for portable - the US Navy Flame Proof Key.

Info

To meet the rugged equipment requirements of naval ships and aircraft, the US Navy commissioned a variety of manufacturers to produce the legendary 26003A Flameproof key. While J.H. Bunnell & Co. eventually became the exclusive supplier for the final three decades of production (ending in 1988), earlier models offer a fascinating mix of origins. You can instantly identify the specific maker of your key by decoding the three-letter prefix stamped into the metal housing of the key (or sometimes the bakelite base), followed by the model number (e.g., CJB-26003A). The first letter “C” stands for “Contractor,” while the following two letters identify the specific company. While Bendix also produced versions of this key (sometimes linked to the code CEA), they are frequently found with different markings. Instead of the standard stamped housing code, Bendix versions often feature a stamp on the plastic terminal cover reading “Type MT-11B”.

• CJB, J.H. Bunnell & Co., New York, NY
• CTE, Telephonics Corporation, New York, NY
• CMI, Molded Insulation Company, Philadelphia, PA
• CMK, McElroy Manufacturing Corp., Boston, MA
• CDM, D.P. Mossman, Inc., Chicago, IL
• CEA, Bendix Radio Corp, Towson, MD

Because the key is designed to be “flameproof” (non-sparking in explosive environments), it does not use a quick-disconnect jack (like a 3.5mm or 1/4" socket) on the chassis, as plugging/unplugging could create an open spark. To connect the key, you must unscrew the sealed cover. Inside, you will find two binding posts or screw terminals where the wires are attached directly. While the key end is hardwired, the other end of the cable would historically be terminated with whatever plug matched the specific radio set (commonly a PL-55 1/4" phone plug or a specific military multi-pin connector), or simply hardwired into the transmitter’s terminals.

Operating Feel

The Navy Flameproof CMI 26003A offers a surprisingly smooth operation, particularly when grounded by a heavy base that allows its sturdy mechanics to shine (I use a 2Lb Straight Key Base “Viewport” from Wally W Jones (W6PPP) @ebay ATTLABMGR). Its fully enclosed, robust design is a massive asset, protecting the contacts and making it an ideal choice for me when travelling.
While there are certainly days when the Junker MT feels slightly more precise, I find that the NFP aligns more naturally with my fist the majority of the time. It hits its absolute sweet spot for me at speeds around 16 wpm, where the tension and travel feel perfectly balanced.