Title: Single SMPC Invocation DPHelmet: Differentially Private Distributed Learning on a Large Scale. Abstract: Distributing machine learning predictors enables the collection of large-scale datasets while leaving sensitive raw data at trustworthy sites. We introduce a learning technique that is scalable to a large number of users, satisfies Differential Privacy, and is applicable to non-trivial tasks, such as CIFAR-10. For a large number of participants, communication cost is one of the main challenges. We achieve a low communication cost by requiring only a single invocation of an efficient secure multiparty summation protocol. By relying on state-of-the-art feature extractors, we are able to utilize differentially private convex learners for non-trivial tasks such as CIFAR-10. Convex learners have proven to have a strong utility-private tradeoff. Our experimental results show that for $1{,}000$ users with $50$ data points each, our scheme outperforms state-of-the-art scalable distributed learning methods (differentially private federated learning, short DP-FL) while requiring around $500$ times fewer communication costs: For CIFAR-10, we achieve a classification accuracy of $67.3\,\%$ for an $\varepsilon = 0.59$ while DP-FL achieves $57.6\,\%$. We also show the learnability properties convergence and uniform stability.