For decoration. Same reason some armies had brass eagles, or spikes, or painted shields, or unit crests on their helmets; decoration. In Vietnam, American GI's wrote griffiti on the cloth camoflage covers which adorned their steel helmets.
yes some have spikes and some don't.some have bumps and others dont
Most of the time if an animal has spikes, they are there to protect them from predictors.
If you're referring to those German leather helmets with metal spikes on their tops, those helmets will almost always fetch about $200.00 or more, even in relatively poor condition. The metal helmets with spikes will go about the same, if they're original.
Track spikes do not have a lot of support for your feet. Some have better support than others. For example, sprinter spikes do not have a heel or an arch. Distance spikes have some cushion for the heel. Overall, it is bad to run in spikes but you can still do it. Some work better than others though. It would be a better idea to run in distance spikes than sprinter spikes.
Leather helmets with spikes atop them. There first steel helmet was the M-16 (Model 1916).
yes
By tying a scarf or some cloth on your head before wearing helmets.
Not all gas masks are compatible with helmets, so some soldiers forgo helmets to wear their masks.
The Echinoderm's body is covered in spikes/spines.Some spines/spikes are long, and some are short.
Spikes on caterpillars are not a sign of cocooning.Rather, they occur only on some caterpillar species.
Geoffrey Spikes has written: 'Reactivity studies of some ti-based metallocenes'