This guide to travelling on the IC / EC services between Denmark will tell you the key things about travelling by these trains.
Accessing the train
Attributes of the train
Which country these trains operate in.
Danish IC trains are now used for this service.
They won't be winning any style awards, but they are comparatively comfortable (when not overcrowded).
If you travel 1st class, once the train arrives in Denmark* jugs of boiling water are provided so that you can help yourself to a complimentary tea or coffee - cold drinks and snacks are also provided.
(*Though this didn't happen on a recent Hamburg - Koebenhavn journey).
Otherwise the difference between 1st and 2nd class on these trains is fairly minimal.
The seats are virtually identical, but the seat arrangements is 2 + 1 in 1st class instead of 2 + 2 in 2nd class, and 1st class has slightly more leg room.
There also vending machines on board for drinks that are available to all, there is no bar/bistro coach or counter.
The trains also have symbols showing that WiFi is available, but this seems to be hit and miss.
It definitely won't be available on the German part of the journey (and may not be available in Denmark either).
Something to look out for is that if you want to use the blinds on these trains, you have to secure it in place, using the pegs attached to the window frame.
Another quirk of these trains is that the trains are arranged into sets of 3 coaches/cars, but in the set of 3 - the middle car/coach has no door.
Reservations are mandatory for journeys between June 11th and Sept 3rd.
When the reservations are mandatory rail pass users will need to pay a reservation fee prior to boarding.
1st class = €5.90; 2nd class = €4.50.
They can be purchased online or at the station, at a Reisezentrum ticket desk.
When booking 1st AND 2nd class tickets on the services on which reservations are required, the seat(s) will be automatically assigned.
At other times of the year, if you book 1st class ticket journey tickets with DB, your reservation is complimentary and seats will be assigned.
However, outside those peak summer dates they're optional when booking 2nd class tickets, or if you will be travelling with a 1st or 2nd class rail pass.
Though making reservations is highly recommended, particularly on Friday - Sunday afternoons.
This is one of more than 150 train guides available on ShowMeTheJourney, which will make it easier to take the train journeys you want or need to make. As always, all images were captured on trips taken by ShowMeTheJourney.