So you create tech to disperse your dispersal units. The problem is you can only blast fuel out so fast, but if you essentially make it a cluster bomb each element can have a reasonable scale. As far as delivery vehicle you don't have to be honest about that to do "testing". Just fly a plane over a prepared site and drop a dud. Japan helped us with little boy. They were ready to surrender. The emperor couldn't say publicly "this war is stupid, let's just stop." By helping us they negotiated us rebuilding Japan and defending them against post-war retaliations.