Those were called "unsubmissive" (insumisos). There was a whole social movement around them, with high-profile court cases and imprisonments. It had (naturally) ties to the squatter movement, the anarchist movement, and the independentists from the Basque Country and Catalonia. The Conscientious objection rates in the Basque Country and Navarra were appalling, by the way.

Those whom the Gods wish to destroy They first make mad. -- Euripides

I was a conscientious objector and then used university deferments to delay my civil service. There was a waiting list of up to three years to get a civil service placement (teh rates of conscientios objection exceeded all expectations) and this led to some uncertainty when joining the labour force, as it was customary for employers to require that you be either exempt from service or had already served, obviously. In the end the civil service was abolished before I had to do it, but not before my last university deferment had expired.

Now, how could you be "unsubmissively" anti-militaristic and also an interventionist?

Those whom the Gods wish to destroy They first make mad. -- Euripides

For Europe I find some interest in the idea of a much wider in scope post-secondary school mandatory service. Some of it would be military, other parts, um, environmental work?? (It's not like I have this well thought out...) This service should be required to take place in a country other than ones home country, and in a language other than ones native one. A kind of enforced, get out, get about, make Europe less foreign. But why mandatory? Why not just encourage young people within existing programmes, and new ones? Well, first there is a  socio-economic factor. (Maybe, I have no data...) But more importantly, mandatory things can have a very beneficial effect in making one do something that one otherwise would prioritise away. Let me bring a personal example:

I went to university in the US. For my undergraduate degree I had to not only take subjects in my major, and related areas, but also in history, anthropology, sociology, literature, art, or rather, I had to pick several subjects from a list of humanities, arts, and social sciences. Subject that I would have never bothered with at the university level, not because I don't find them interesting, but because under a system where it would be allowed but not required I would have felt compelled to concentrate on what directly mattered to my future occupation.

(For all the terrible things I have to say about the US, I really, really like their broader undergraduate curriculum. Going to university there was quite simply great. Maybe not true for all schools??)