Hammarlund was a very old company, and something of a pioneer. It was founded in the 1920s, by Oscar Hammarlund in Manhattan. Its initial Comet Super Pro line led to the legendary SP- series of comm receivers, that was made, by the thousands, until the 1970s. Later on, Hammarlund introduced the HQ- line of receivers at a more affordable price for hobbyists. These, too, were made by the thousands, until the early 1970s.
The HQ- receivers were large, in the real boat anchor style. The Hammarlund HQ-140X had those ominous, gun-port-like, little holes through which you read the dials (the Super-Pro commercial/military series had these too). Later HQ- models were more generally streamlined, still large boxes, but hardly heavyweight ones, with bigger openings.
Hammarlund got into transmitters in the 1950s and 1960s, with its HX- series. The first ones were obviously intended as companions to the HQ- line of receivers, as the cases are quite similar.
Hammarlund's top line, the Super Pro series, is the kind of thing that makes radio freaks drool. It never changed that much. It just got better. The best one is the last one, the redoubtable Hammarlund SP-600. Following the Collins R-390/URR, it's probably the receiver that defined the boat anchor scene.
In the end Hammerlund, as many others, couldn't make the transition to solid state gear. The factory closed around 1972, and that was that.