These Stio Tipton Tech half zip long-sleeve shirts are a great baselayer. They're made of a polyester/cotton/spandex blend that wicks moisture 4x faster than cotton. This half-zip comes in two colors, each featuring the RAF logo on the front:
Inferno Heather - a reddish orange with a lighter orange RAF logo (both men's and women's)
Orange - a standard orange with a grey RAF logo (men's features a blue zipper, while women's features a pink zipper)