Observers have noted that this is plenty of room for a couple of spy satellites. An image of the craft may be seen here.
The X37 program has been in development since 1996 and is the combination of two programs - the X40 inaugurated by the Air Force and the X37 (originally called Future-X and implemented by Boeing) by NASA . The projects were combined in 2000 under NASA's supervision, with original plans to carry the X37 craft aloft inside the Shuttle, thus dictating the maximum wingspan.
In 2003, the project "no longer fitted its long term agenda" according to NASA, and was transferred to the Department of Defence's Advanced Research Projects Agency. By November 2006, the project had completed a full circle and was back with the Air Force.
The X-37B OTV's (Orbital Test Vehicle) objectives will be "risk reduction, experimentation, and operational concept development for reusable space vehicle technologies, in support of long-term developmental space objectives."
Clearly these are the objectives of the US Military.
"Getting it into orbit, getting the payload bay doors open, the solar array deployed, learning about on-orbit attitude control and bringing it all back."
Commenting on speculation that this craft is one further step in the weaoponisation of space, Payton responded, "I don't know how this could be called weaponisation of space. It's just an updated version of the space shuttle type of activities in space. We, the Air Force, have a suite of military missions in space and this new vehicle could potentially help us do those missions better."
On the basis that many Shuttle missions are undertaken on behalf of the Military, that would be a 'yes.'
The 5 tonne craft is powered by extensible solar panels and has a small rocket engine for orbital manoeuvrers and to permit re-entry.
Upon re-entry the X37A will land itself at the 4,500m main runway at Vandenberg Air Force Base in California. Hopefully without human help; and without incident.