I was always taught that it was a small letter ‘d’ EXCEPT at the start of a sentence..

As in….

The de Havilland Mosquito attacked Amiens…..

De Havilland Mosquito’s attacked Amiens ……..

It’s a confusion, but no, as the ‘de’ is a name it should remain lower case even at the start of a sentence. Of course it’s therefore a good idea to start your sentences with a different word to avoid the problem.

The only times it should be a capital ‘D’ are when the whole word has been written in upper case: ‘DE HAVILLAND’ or in the abbreviation: ‘DH’; not ‘dH’

BTW, Apostrophes are for the possessive, not the plural.

All the points have been covered in the previous discussions in the links provided. 😉