Nauticalia

The brass body of this pen is made from a genuine .375 H&H Mag case (typically used for game hunting), which makes it rather more interesting to look at, and tactile, than a mass-produced plastic tube.
 
But it’s also much better than “normal” pens, as the special ink inside is pressurised so that you can write on any surface – even upside down or underwater – using technology developed for NASA.

Medium point, black ink, length 4”.