Linked to the maritime world since the 18th century, where it appears in English and Dutch paintings, it is only in 1858 that a state order imposes the marinière as an official costume for sailors.
A precise number of stripes and widths is then defined to the nearest millimeter: 21 white stripes 20 mm wide and 21 blue stripes 10 mm wide for the chest and, for the sleeves and always alternating white and blue, 15 stripes maximum.
It is said that the number 21 was chosen as a reminder of Napoleon's victories and that the stripes allowed to spot a sailor at sea. In reality the reasons were much more pragmatic: indigo was very expensive for the time, the use of white allowed to save money.