NATO has a mobile unit that can deploy very rapidly.

Judge as of 2015. TRUE: NATO had a standing or high-readiness military unit able to deploy at short notice, for example the NATO Response Force or the Very High Readiness Joint Task Force set up in 2014–2015, deployable within days. MOSTLY TRUE: NATO had such a force, but its readiness or speed was somewhat slower or less complete in 2015 than 'very rapidly' suggests (for example, the VJTF was still in its interim phase). MIXED: NATO had a rapid-reaction force only on paper, or with readiness widely judged doubtful. MOSTLY FALSE: NATO's rapid forces existed only as plans not yet available in 2015. FALSE: NATO had no rapid-deployment mobile force in 2015.

Set before the research began.

1. E1 Statement by the NATO Defence Ministers on the Readiness Action Plan NATO · 5 February 2015

   “its flagship element will be a new Very High Readiness Joint Task Force (VJTF), centred on a multinational brigade with up to five manoeuvre battalions with some elements ready to move within 2 to 3 days.”

2. E2 Statement by the NATO Defence Ministers on the Readiness Action Plan NATO · 5 February 2015

   “We also welcome the availability of the Interim VJTF capability for 2015 led by Germany, the Netherlands and Norway, with some other Allies participating, which has already started training and exercising.”

3. E3 Statement by the NATO Defence Ministers on the Readiness Action Plan NATO · 5 February 2015

   “Today, we agreed to enhance the NATO Response Force, which will become a division size joint force with significantly increased readiness”

NATO defence ministers said in February 2015 that the NATO Response Force already existed and would be enhanced into a division-size joint force with significantly increased readiness (E3). The statement also said its flagship element would be a new Very High Readiness Joint Task Force with some elements ready to move within 2 to 3 days (E1). For 2015, though, the capability available was an Interim VJTF led by Germany, the Netherlands and Norway, which had already started training and exercising (E2). So NATO did have a rapid-deployment force in 2015, but the very-high-readiness version was still in its interim phase, which matches the criteria's example for mostly true.