Stefanie, I am a hobbyist who enjoys studying WWII, and sharing history/research info with other novices. Until you receive a response from an expert researcher, or until you secure the services of a professional, here is some info you might be able to use. Some are resources I have used researching my own family, others are those I have only read about, or found online. Please be sure to verify all to your own satisfaction.
You should be able to get his personnel record through the NPRC in St. Louis. (They had a disastrous fire in 1973. However, they indicate that Navy Dept personnel records were not affected.) Info on that resource can be found at this web page: http://www.archives.gov/st-louis/military-personnel/index.htmlhttp://www.archives.gov/st-louis/military-personnel/index.html
You can also send for his Individual Deceased Personnel File (IDPF). As others in this forum have addressed, the info found in an IDPF can be graphic. If you pursue this resource, you should be prepared for that possibility. Send your request to: US Total Army Personnel Command ATTN: TAPC-PAO (FOIA) 200 Stovall Street Alexandria, VA 22332-0404 Be sure to cite the Freedom of Information Act in your request. (The above references "Army" but personnel at this command told me via telephone that they also hold Navy/Marine IDPF's for WWII.)
Another resource I have read about, but have not used: Information on personnel who may have died while in the U.S. Navy is recorded on index cards. A description of how the individual was killed is usually included. These may be requested from: Officer in Charge Naval Medical and Dental Affairs Mortuary Affairs Branch PO Box 886999 Great Lakes, IL 60088-6999 Phone 800-876-1131 Ext. 621, 627, or 628 Fax 847-688-3964
There would be no "circumstances of his loss that merited a Purple Heart". A PH is awarded for a wound received in combat. All service men who are killed in action receive a PH, posthumously.
One observation I made which is worth mentioning, I believe: In your post you cited his serial number as, "263989". I looked him up in the American Battle Monuments Commission (ABMC) database. His SN is listed there as "0-263989". That zero is part of his SN. (It designates him as an officer.) Be sure to list it when requesting records, etc.
The ABMC says he also received an Air Medal. Evidently he was a Navy flier. If that was the case, there may be other resources available (such as a Missing Air Crew Report - MACR) which would tell you more of his story. However, the experts I alluded to above will have to help you in that regard.