The article says "will send", but my understanding is that a U.S. Air Force B-52H (callsign Moose 51 from the 5th Bomb Wing, MT/60-0055) and a KC-135 have arrived at Royal Australian Air Force Base Darwin today to take part in short term joint training with the RAAF. The B-52 is assigned to Andersen AFB as part of U.S. Pacific Command and U.S. Air Force rotational presence in the Pacific, and the KC-135 is part of the Tanker Task Force in the region.
B-52s in Darwin are unusual, but not all that unusual. The last B-52 visit to RAAF Darwin was in 2010, when they took part in Exercise Hamel with the Australian Defence Force. The B-52s also conduct missions to use the Delamere range, usually round-trip missions from Guam without stopovers.
Indeed, a B-52 from the 69th Expeditionary Bomb Squadron was the sole USAF participant in 2012's Exercise Pitch Black held in Australia's Northern Territory, staging from Guam and being escorted by "Taiwanese" (NOTE: Most likely Singaporean as Taiwan does not participate in Pitch Black) and Indonesian fighters (presumably Singaporean F-15SGs and Indonesian Su-27/30s as part of Blue Force) on it's way to and from target. I'll need to look deeper into this, but I'm pretty sure this marks the first time a B-52 has been escorted by Flankers on a mission, albeit on an exercise.
What caught my eye was this bit from the first link: "...decisions on future rotations are still under discussion. One of the goals of this visit is to discuss details required for support to future rotational deployments to both RAAF Darwin and RAAF Tindal."
Various sources have indicated that in the near future, rotations of USAF and US Marine Corps air assets to Northern Australia may become semi-permanent or even permanent as part of the "pivot to the Pacific". This current deployment to Darwin may only be the start of many more to come.
Thanks to William Nguyen Phuoc for additional information