At least five countries reached a working radio-echo detection system independently within a few decades of each other, so the question is which milestone, a working principle, a working military system, or an operational network, defines "invention."
What would resolve this A settled convention for what counts as the invention of a multi-national simultaneous-discovery technology, comparable to how the field already treats the telegraph and telephone priority disputes, would resolve this the same way.
OpenHistory of technologyWikipedia contributors, Radar (Wikipedia)