As long as the weaponry is not too outdated, I believe the Vietnamese army can withstand for a period of time.
After all, not all of the French mobilized troops are composed of native French armies; there are still many indigenous troops mixed in.
If Vietnam and the country behind it are willing, Spain could even sell warships to them.
From Spain's two models of ironclads to various cruisers and coastal defense ships, these are all available for sale.
To catch up with the war, Spain could even sell the currently active navy ships. After all, Spain's shipbuilding plans are steadily building ironclads and other warships; selling old ships to build new ones is profitable for the Spanish Navy.
Following Carlo's orders, sales personnel from the Royal Military Factory traveled across the seas to Southeast Asia, not only carrying some of the weapons and equipment data Spain could sell abroad but also bringing images of Spain's active-duty warships.
