Some occupations are regarded by the law as so intrinsically dangerous
that those who follow them can make a will
by simple declaration, without the other formalities such as writing, testator
's signature, and signature of witnesses. The situations affected are going to war
and going to sea
This is known as a privileged will. It is a long-standing part of English law, and though it might well have been amended in other jurisdictions inheriting English law (I am not a lawyer), it is current in the law of England and Wales.
The first group allowed the privilege are soldiers on active service. Not necessarily in the heat of battle: they might make their will calmly at local headquarters, but if they are somehow in the field or warzone, they are so privileged. And it need not be a regular war: service against terrorist gangs in Northern Ireland counts.
The second group are seamen at sea. This doesn't just mean sailors in the Navy, but anyone whose occupation takes them out there: bartenders on a cruise liner, for example, though not the passengers. They need not be in imminent danger. As soon as the ship leaves the dock it becomes the site of this privilege.
It is a general legal principle that anyone in articulo mortis (on the point of death) can give away any of their property that can be just given away: this donatio mortis causa (donation because of death) does not however cover things such as houses or cars, which require transfer by deed. And this giving away is just that, immediate disposal of goods: it is not a will, and does not make any other such provisions as a will might.
In contrast, a privileged will is a valid legal will in the full sense. A soldier shot by a sniper, having only the breath to gasp out, 'If I don't make it, make sure Ann gets all my stuff', thereby makes a will, which revokes his previous written, signed, and witnessed will. This will really does cover everything, houses and land and all, just as a written one does.