The DW-6600 is a model issued to the us navy seals in recent times, appearing in 1994 it was favoured by the military due to its reliability, light weight, and low cost. The 6600 is also notably known for its el backlight, which illuminates the whole display, this bad boy effectively replaced the Rolex sub, but has since been discontinued by Casio in late 2010 with stocks running into 2011. The chevron thingy I have no idea, but am pretty sure the date is when it was issued
~Benji