10 Dollars - Princess Joan I Jubilee

Sealand's claim to nationhood rests on a 1968 occupation of HM Fort Roughs, a Royal Navy sea fort seven miles off the Suffolk coast, by Paddy Roy Bates, who declared himself Prince Roy I. Britain's own courts inadvertently bolstered the claim when a 1968 ruling found that the fort lay outside UK territorial jurisdiction. The "Principality" issued coins primarily as revenue, not for any functioning economy — there were never enough residents to circulate them.

X#3.1 places this squarely in the fantasy/semi-postal issues tracked by Krause's Unusual World Coins, the only major reference that catalogues Sealand pieces at all.