Delta announced this last month an order for 40 Airbus Aircraft. Ten of which will be A330-300 variants to supplement their international capacity. The remaining 30 will be A321 aircraft. The order timeline shows them arriving between 2015 and 2017.
For a more detailed breakdown of the arrival and retirement schedule this website uses please see the supporting spreadsheet. As always we welcome contributions/corrections about aircraft order and retirement specifics.
The impact of these aircraft orders has been updated on the websites Delta Airlines Pilot Demand page. Delta's press release did not indicate any aircraft retirements. However with their strict capital discipline it is possible that they could retire some older aircraft as they bring these airplanes on property. These retirements would affect the number of pilots needed.
For Delta's press release please see the following link.