T-Mar

They're called truss forks. The earliest example is likely the mid-1890s Pedersen bicycle, though these did not catch on. The style was subsequently used on early motorcycles and the bicycle industry took their lead from that. They were popular on American bicycles from the the Great War period though the 1950s, when it was popular to have bicycles styled like motorcycles, with faux gas tanks, double top tubes, axle mounted kickstands, etc. The leading truss strengthens the fork while allowing blades of smaller diameter and thinner material, without the forks collaspsing. Basically, it gives the best strength to weight ratio.