Here we see men of the BEF’s Royal Irish Fusiliers on the march at Gavrelle, near Arras, 17 October 1939, 80 years ago today. The two men in the foreground are carrying a Boys anti-tank rifle Mk I.
Chambered in Kynoch & RG .55-caliber Boys, the beefy panzer zapper weighed 35 pounds and was effective when it was designed in 1937 as it could penetrate 23.2mm of armor 100 yards and 18.8mm out to 500 yards, capable of taking on early German tanks (e.g. the Panzer III Ausf. A through C generations only carried 15mm of armor all around).
However, as the war wound on, it became increasingly relegated to other anti-material uses as early RPGs took over the tank-busting role.