Yes, if America decides to try and move through SZ 60 with those ships in the combat movement phase, they will have to stop and engage the defending enemies. However, if you clear them out and then try to move your ships through on non-combat they can sail through.
New units
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Where to buy new kind of units? I want also a description of the unit like attack defense andfeatures
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Check this site: http://www.historicalboardgaming.com
There are no rules for those extra units. You have to make them yourself. But then you can better go to the forum for house rules.