When talking/writing about past ability you can use 'could' or 'was/were able to' in order to discuss an ability that existed for a long time, but now no longer exists. Examples: ... But you should only use 'was/were able to' with action verbs to talk about an ability related to a single event or incident in the past.

Could and was able difference?

If you say that someone was able to do something, you usually mean that they had the ability to do it and they did it. Could does not have this meaning. After two weeks in bed, he was able to return to work.

When to use could VS able to?

We sometimes use be able to instead of "can" or "could" for ability. Be able to is possible in all tenses - but "can" is possible only in the present and "could" is possible only in the past for ability. ... So we use be able to when we want to use other tenses or the infinitive.