By World War Two machine guns were more mobile and adaptable weapons, whilst sub-machine guns gave infantrymen far greater potency at close quarters. They were also fitted to tanks and aircraft, although became less effective in these roles as Armour plating improved. The machine gun therefore went from determining the static tactics of attrition used in World War One to being a fundamental part of the mobile tactics more common in World War Two https://matthewmeierphoto.photoshelter.com/gallery-image/Solomon-Islands-Photos/G0000cDI7NovHBU8/I0000wCWtZW4Yn7s
A gas mask is a mask used to protect the wearer from inhaling airborne pollutants and toxic gases. The mask forms a sealed cover over the nose and mouth, but may also cover the eyes and other vulnerable soft tissues of the face. Most gas masks are also respirators, though the word gas mask is often used to refer to military equipment .The gas mask only protects the user from digesting, inhaling and contact through the eyes (many agents affect through eye contact). Most combined gas mask filters will last around 8 hours in a nuclear biological chemical (NBC) situation. Chemical specific filters can last up to 20 hours in a NBC situation. https://en.wikipedia.org/wiki/Gas_mask
FOR DECADES, THE BATTERED TRUMPET RESTED NEARLY 100 FEET BELOW THE OCEAN’S SURFACE IN A PILE OF BULLET CASINGS HIDDEN WITHIN THE WRECKAGE OF THE HOUSTON, UNTIL AN AUSTRALIAN DIVER EXPLORING THE SHIP NOTICED IT DURING AN EXPEDITION IN 2013. HE TOOK THE TRUMPET, BUT LATER, AFTER REALIZING HE HAD TAKEN IT ILLEGALLY, HE REACHED OUT TO THE NHHC’S UNDERWATER ARCHAEOLOGY BRANCH TO APOLOGIZE AND RETURN IT, RUANE WRITES. https://www.smithsonianmag.com/smart-news/trumpet-retrieved-world-war-ii-shipwreck-could-still-hold-its-owners-dna-180958037/
Firstly, when under shell fire, the instinct is to curl up and bring your head down. When you do this, your head rotates forwards, exposing the back of the neck. Angling the helmet all the way backwards offers more protection from the back of the neck, and generally maximizes protection from above at that head angle. This suggests a more backwards angle, such as seen on the guy in the foreground here.
But sometimes helmets are angled the other way as well, such as the chap lighting a fag above (again WWI, but in terms of helmet nothing really changed). On this one I'm not too sure. Maybe it's just fallen down and he can't be arsed to right it. Maybe he was just resting against that side of his head. Or maybe even the image has been flipped.
http://ww2germanhelmets.com/Information-German-WW2-Helmets.com.html
But sometimes helmets are angled the other way as well, such as the chap lighting a fag above (again WWI, but in terms of helmet nothing really changed). On this one I'm not too sure. Maybe it's just fallen down and he can't be arsed to right it. Maybe he was just resting against that side of his head. Or maybe even the image has been flipped.
http://ww2germanhelmets.com/Information-German-WW2-Helmets.com.html