[Slonopotam845]

Designing a workable bomb is not that hard. Making a reliable one is hard. In fact workable designs are so well understood that we don't have to test them anymore. Rail-gun designs like the Hiroshima bomb are very well documented and you could with some physics background pick a lot of the parameters off a table. Now collecting enough fissile material and machining and engineering the device even a crude device is much harder. But you would end up with is entirely functional. If you had the material you could build a device in the 8-15kt range and it would be deliverable somehow. Whether by truck or plane or cargo ship. Since these kinds of devices aren't really intended to stand off in an inventory one doesn't need sophisticatd PALs (passive access locks) those highly secure cryptographic ignition control switches that serve as fail-safe devices. Now ideally one wants to air drop a small warhead and have it detonate about 300-400 meters above ground but if that's not possible and it's a ground burst - the effective blast radius would still be pretty large.