The origins of the bush hat go back to the introduction of the '44 pattern 'Jungle Green' uniform that was used throughout the 1950s and '60s before the introduction of the DPM tropical suit. The hat, however has remained unchanged apart from the DPM manufacture.
At one time they were very hard to find and possession of one marked the individual out as either being one of them, someone who'd been to a hot posting like Belize, Hong Kong or Cyprus, or (more often than not) someone who was simply a big-timing walty cnut who'd been shopping at Silverman's.
The variation of styles that can be achieved by their wearers is quite staggering. RLC mongs and RAF techies tend to adopt the 'Eastwood', whilst anyone worth their salt either alters theirs by cutting down the brim (the origins of this date back to Malaya, when peripheral vision was enhanced), or purchases a tailored SF-style example available from several commercial suppliers in that never ending pursuit of allyness. Since 1990, the bush hat has been produced in desert pattern DPM.
Old school types fold the brim under the crown to resemble the DILAC Hat.
Get the low down here.