This question already has an answer here:
In the beginning of Avengers Age of Ultron movie, Avengers attack Strucker's base and there Stark discovers the corpse/skeleton of the big Chitauri whale that attacked NYC in the first Avengers movie. That the skeleton is indeed likely of the Chitauri whale is further reaffirmed when it comes alive in Stark's vision as part of the Chitauri fleet attacking earth.
Was Strucker trying to create those Chitauri whales himself? It doesn't sound logical because that wouldn't work without the alien technology, troops and tactics etc that Chitauri employed.
Did Strucker import it from US? If so, how? There were only 2-3 of them and each was big enough to not go unnoticed.