Complex sentence: On 17 January, Ingenohl ordered "Helgoland" to go back to the docks for more maintenance, but she didn't enter the drydock until three days later, owing to difficulties getting through the canal locks.
Split into simpler sentences: On 17 January, Ingenohl ordered "Helgoland" to go back to the docks for more maintenance. It wasn't until 20 January that the ship successfully entered the drydock, owing to difficulties getting through the canal locks.