It is fairly well documented that in 1934 the US Navy issued the requirement for a new Scout Bomber. This was at the time the Navy was starting the transition from biplane to monoplane aircraft.
The XSB3U-1 was built as hedge against the Navy not accepting the XSB2U-1 Vindicator in the 1934-35 time frame. There was discussion about monoplanes being too large to handle on deck, high approach speeds, and longer take-off distances, some of the same arguments in the discussion of progressing from propeller driven aircraft to jets just about 10 years later.
The top speed for the XSB3U-1 was listed at 215 mph which meant the retractable landing gear bought approximately 10 mph over the previous SBU-1/-2 aircraft that it was intended to replace. That speed was a good 30 mph slower than the SB2U-1.
One XSB3U-1 was built and the contract went to Vought to build the SB2U series. Here is a general arrangement for the XSB3U-1 from the Vought Heritage Archives
In the end the XSB3U-1 was the last vestige of the biplane dive bomber line at Vought that started with the end of another era, the two seat fighter (pilot and rear gunner) XF3U-1. The XSBU-1 was the XF3U-1 prototype re-purposed into the dive bomber series SBU-1 and SBU-2.