## 1 Introduction  
The Fourth Industrial Revolution, also called the Industry 4.0 paradigm, represents the digital transformation of factories in terms of people, processes, services, and systems to increase competitiveness and offer a customer-centered value. The term was originally coined by the German government in 2011 [1; 2]. One of the foundations of Industry 4.0 consists of gathering as much data as possible from the value chain and acquiring intelligence to drive smart manufacturing. Another aim is to achieve the convergence between the physical and digital world through solutions like cyber-physical systems or digital twins [3]. A digital twin can be defined as a virtual representation of a physical asset enabled through data and simulations for real-time monitoring and actuation during operation [4]. With the objective of providing such a level of interconnection, smart factories rely on communications architectures that enable information exchange among multiple industrial devices distributed throughout a factory, autonomous decision-making processes, and end-to-end supply chain traceability. The Industry 4.0 paradigm makes use of relevant disruptive technologies. Examples of such enabling technologies are cloud and edge computing [5], blockchain [6], artificial intelligence [7], the Industrial Internet of Things (IIoT) [8], robotics [9], and Augmented Reality (AR) [10]. Under the Industry 4.0 paradigm, shipbuilding companies are updating and integrating new technologies in their working processes. Among the enabling technologies that can be used in a so-called Shipyard 4.0 [11], one of the most promising is AR, specifically Industrial Augmented Reality (IAR), which provides a wide range of features that can be leveraged in order to develop powerful and useful applications able to show virtual elements in real scenarios. Navantia, one of biggest European shipbuilders, created with the University of A Coruha (UDC) a Joint Research Unit Navantia-UDC to design, to implement, and to validate different Industry 4.0 technologies through various research lines. The authors of this article work in a research line called \"Plant Information and Augmented Reality\", devoted to analyze the potential of IAR applications for Shipyard 4.0. AR's first developments appeared in the early 1960s with the experiments of [PERSON] [12]. In the 1990s, AR gained some traction as a technology that allows for mixing the physical and digital world through natural interactions and 3D models. Recent advances in software and hardware capabilities enable developing high-quality and cost-effective AR experiences with different devices, from simple low-cost smartphones to very sophisticated Head-Mounted Display (HMD) devices. Industry 4.0 AR applications are relatively new in comparison to entertainment [13] or gamification [14] applications. This is due largely to the more restrictive requirements in tracking, registration accuracy, and end-to-end latency, as well as to the specific characteristics of industrial environments. IAR can help to improve industrial processes, to maximize worker efficiency and mobility, and to incorporate new learning and training procedures such as blended teaching and digital near-the-job trainings [15]. Such trainings can reduce costs and time, increase safety, and adapt to different learning spaces and experience. Although the advantages of IAR technologies have already been empirically validated [16; 17; 18], there are currently only some early works that apply such technologies in a collaborative and targeted manner in production environments [19]. This article presents the analysis, design, implementation, and evaluation of a smart glasses-based IAR application aimed at training and assisting Navantia's operators in assembly tasks. In contrast to our previous work [20], which was mainly focused on describing the developed application, this article focuses on the embed collaborative framework and the evaluation of its performance.