Pretty cool!
Here's the official cursory info for them I can scrounge up:
18. Cardisoma armatum Herklots, 185 1
COLOR: Young, newly molted individuals with violaceous carapace; tips
of chelae and walking legs bright red; with age and approach to molt carapace
turns dirty yellow with occasionally slight reddish spots dorsally.
DISTRIBUTION: Western coast of Africa from St. Louis to Baia dos
Tigres, Angola, Africa and Cape Verde Islands.
HABITAT: Moist sandy areas above the mean high tide level; mangroves,
mouth of rivers, under houses, in cultivated areas adjacent to permanent
sources of brackish or sea water; and inland areas of larger islands.
HABITS: Youngest juveniles are in small depressions or newly dug
shallow burrows directly adjacent to water; older juveniles found in smaller
compartments within the burrows of adults. Adults construct deep burrows,
and often these are part of a large colony where the burrows intersect. Adults construct
burrows of varying depth and structural complexity, depending upon their
age and the location of the burrow with respect to available ground water. Both
juveniles and adults are nocturnal scavengers, often moving considerable
distance from their burrows to feed on palmnuts, coconuts, dead fish and
scraps of vegetation. Spawning activities have not been recorded in the
literature for this species.
COMMON NAME: Edible land crab.
REFERENCES: Barnard, 1950 (D,T) ; Cheesman, 1922 (B), 1923 (B) ;
Dalziel, 1920 (D); Rathbun, 1921 (D,T) ; Wanson, 1935 (D).
From:
A SYNOPSIS OF THE BURROWING
LAND CRABS OF THE WORLD and LIST
OF THEIR ARTHROPOD SYMBIONTS
AND BURROW ASSOCIATES
By DONALD B. BRIGHT AND CHARLES L. HOGUE
For patriot crabs, since it is a bit difficult to maintain deep burrows that intersect the water table for most typical hobbyists' tanks, the simplest but best way to keep them is to keep one per tank (they can be pretty aggressive towards each other).
Then the tank set up should be of smooth gravel (yep, gravel), but setup so it's sloping - something like this (sorry for the crude drawing:)
The tank you have right now would be fine temporarily, but eventually I would make the switch to the smooth gravel type setup. (On a side note, the tank you have right now is actually recommended for Halloween crabs, like mine, but not for Patriot crabs for long term keeping.) Patriot crabs will need to immerse themselves in water for molts, something that the land hermit and land Halloween crabs do not need to do. The crab will also end up digging out the sand, attempting to dig down to try to find a nonexistent water table and generally making a swampy mess of the sand setup - a gravel setup would be somewhat easier to maintain for the home tank.
For the water, I'd make it brackish, as I've had one molt with me in the brackish water part of my aquarium in the water (unlike land hermit and land Halloween crabs, Patriot crabs need to molt in the water). I'd make the specific gravity around 1.010-1.020 and the pH about 7.5-8.2.
You can put an airstone or a small sponge filter in the water part of the tank to keep it aerated or filtered.
For food, they are known to be scavengers, so they can be fed the same food you are feeding the land hermit crabs, but their main diet is composed of leaf litter, so unlike land hermit crabs, you may need to add more leafy greens to their diet - like spinach leaves, for example. I would also provide cuttlebone as well.
Here's a pic from a German website of one of the armatum tanks:
http://www.panzerwelten.de/v/Cardisoma/ ... 6.jpg.html
...and will eventually lose their "Patriot" colors....
But that's for a long time, so no worries, yet...
I hope you won't eat him, Nota! 
