You are not required to regularly return to the country to which you have personal ties if you reside in Denmark exclusively for the purpose of practicing a profession for a limited period of time.
In this case, you will be regarded as having usual residence in the country to which you have personal ties.
The first ship commissioned by the US Navy was Bluebird, this is where the US ships got their class name.
With slight changes in design, some of the ships are referred to by other class names, such as Falcon class, Redwing class, Albatross class, or even under Adjutant class.
Usual residence means that you have personal or occupational ties to Denmark i.e.
that you spend a minimum of 185 days in Denmark within one calendar year.
If you have a foreign driving licence and you have established usual residence in Denmark, you must in certain cases exchange your driving licence for a Danish driving licence.