The Douglas Dauntless, called with affection the "Speedy D", was the plane that broke the Imperial Japanese Navy's neck in 1942. I was advised by Eric Bergerud in an Email conversation that I could hardly overestimate the importance of this plane.

    Its history began when the Navy in 1934 asked for offers for an low-altidute bomber with the ability to dive. Northrop,  having only recently left Douglas, offered the BT-1, and the Navy, after having seen it fly, order 54 machines in 1936. But flight tests on USS Yorktown and Enterprise showed serious problems with this plane, finally canceling its use.  
However, the contract with the Navy foresaw also the continued development of the BT-1, and Northrop continued it by putting a Wright-Cyclone engine in and calling the result the XBT-2. Further testing reveled other flaws, and finally, Northrop had a nice plane, and left any connection to Douglas behind.

    At this time, Douglas bought Northrop Corporation, and the plane was renamed XSBD-1, and named Dauntless.  
A first batch of  these planes, of the SDB-1 type, was bought by the Marines. 57 planes were build.  
Douglas continued the design by adding more fuel tanks, making the SDB-2, which was first brought to sea on USS Enterprise and USS Lexington. In addition, the SDB-1 was deemed okay for sea operations.

    Over the time, Douglas build more variants. The SDB-3 was using self-sealing fuel tanks, and improved armor protection for the crew. Part of the 580 planes of this batch came from a order of the French Air Force, cancelled by German tanks. Interestingly, the Free French Air Force, after the liberation of the better part of France, came to use several dozend Dauntlesses in the air support role until the German surrender.

    The versions of SDB-4, -5, and -6 added more details of improvement, and when the production ceased in 1944, 5936 planes had been been build. The Dauntless won tremendous successes. Dauntlesses participated in the sinking of all six Japanese carriers lost in 1942, sinking four by themselves alone. Another two cruisers were their preys, plus many destroyers, transports, and submarines. Numerous small craft were also part of the score board.