Wood, metal or plastic?  The choice is  entirely yours.  I personally prefer wood or bamboo as they are 'warm' to the touch and not as slippery as metal.  
Metal knitting needles are great if you are a 'tight' knitter as they allow the yarn to slide more freely along the needle which is great if you are using straight long needles, and are knitting flat, but I find them impossible to use if I am watching tv at the same time as I have dropped too many stitches that way!
Plastic are light and flexible, warm to the touch but can snap easily and may be too bendy when there is a lot of yarn weight on the needles.
My personal preference is for wood or bamboo circular needles and I will post recommendations on the resources page.
The reason I prefer circulars, even when knitting flat is that the weight of whatever I am knitting rests in my lap and not on the needle and does not give me wrist strain.
They are an investment but will last forever and you can buy a single pair of fixed circular needles to see if you like them.

 

As mentioned in the previous needle chat, my preference is for circular needles.  I have three sets of interchangeable needles with varying lengths of cord.  I also have several sets of 'fixed' cord needles which do not need the fiddly key to tighten the pins to the wire.  
If you have arthritis or rheumatism or grip issues, these kinds of needle allow the weight of the knitted garment to rest on the cable rather than on the needles and ultimately on your wrists.  There are also some rather funky 'cubic' needles which are square rather than round and are specifically designed for those with grip issues and rheumatism/arthritis.
DPNs or Double Pointed Needles are most useful for sock knitting and knitting smaller items in the round.  I knitted the first three hats 'flat' and then got fed up with mattress seaming so I have now taught myself to knit 'in the round' and love it!
I already had a couple of sets of DPNs that came as freebies with my circulars and they are invaluable when getting to the last few stitches at the top of a beanie.
For those of you who are interested, I will be posting a series of links to YouTube videos showing all these techniques for both left and right handers.
 

Mattress Stitch is much the best way to join the hat if you are working 'flat', as it results in a really smooth join that will not be lumpy or dig in under a helmet.  The link below will take you to a slow motion video of how to sew the hat up using mattress stitch.

https://www.youtube.com/watch?v=wQnAfTmI0iA
 

Yarn specified for this project MUST BE BLACK, ARAN OR WORSTED WEIGHT & WASHABLE.  After that, it is up to you.  Yarn can range from £1.99 to the sky's the limit BUT bear in mind it will need to be worn next to the skin;  so try to find a yarn that is relatively smooth and Not too fuzzy as the fibres could get in the soldiers' eyes.
The reason for the specific weight is to create a soft but hardwearing beanie that provides the correct level of insulation between the head and a helmet. 
I will link several online companies and my yarn recommendations on the. resources page.

coming soon

coming soon

coming soon

coming soon

coming soon