We have observed superconductivity in platinum powder compacts with grain sizes in the submicrometer range at transition temperatures and critical magnetic fields as high as 20 mK and 18 mT. These values are more than one order of magnitude larger compared to our previous results for samples with larger (micrometer) grain size. For a better understanding of the superconducting properties of the granular platinum samples, we have also investigated various properties in the normal state. The submicrometer samples exhibit strong lattice strain and significantly smaller Debye temperatures compared to bulk platinum. Moreover, the ferromagnetic spin fluctuations of the conduction electrons are partially quenched in these compacts. On the basis of these results, we discuss the origin of superconductivity in granular platinum.