Analysis of information sources in references of the Wikipedia article "Lockheed P-38 Lightning" in English language version.
Gun, Automatic 37-mm T9- The T2 gun was modified... until eventually a gun designated T9 was ready for test. In September 1939 this gun was mounted... in P-38 and P-39 fighter planes... which was standardized as the M4.
...the 418th, 419th and 421st Night Fighter Squadron were given P-38s.
Another experiment was the modification of P-38 40-744 for pilot asymmetric flight tests...
By some accounts, P-38 photo missions brought back 80 to 90 percent of all aerial recon photos from that period...
90 percent of all aerial reconnaissance film taken during the war in Europe was captured by smooth-flying P-38s