This was an event that was not widely reported due to the Trinity Test happening at the same time.
The
US Navy's Aug. 15, 1945 news release on
the loss of the USS Indianapolis (and ca. 880 lives) was indeed pushed to the newspaper back pages by a more notable news release.
However, the overshadowing news release was not the
Aug. 7, 1945 news release of the
July 16, 1945 Trinity Test, but
the news of Japan's surrender released 7 PM, Aug. 14, 1945.