Dates used for sorting will rely on EN-US standard, display will relay on user's culture.

NzbDrone.Web/Controllers/HistoryController.cs

@@ -37,6 +37,7 @@ namespace NzbDrone.Web.Controllers
                 Quality = h.Quality.ToString(),
                 IsProper = h.IsProper,
                 Date = h.Date.ToString(),
+                DateSorter = h.Date.ToString("MM/dd/yyyy h:mm:ss tt"),
                 Indexer = h.Indexer,
                 EpisodeId = h.EpisodeId
             }).OrderByDescending(h => h.Date).ToList();

NzbDrone.Web/Controllers/MissingController.cs

@@ -31,7 +31,7 @@ namespace NzbDrone.Web.Controllers
                 EpisodeTitle = e.Title,
                 Overview = e.Overview,
                 SeriesTitle = e.Series.Title,
-                AirDate = e.AirDate.Value.ToString(),
+                AirDate = e.AirDate.Value.ToString("MM/dd/yyyy"),
                 AirDateString = e.AirDate.Value.ToBestDateString()
             });
 

NzbDrone.Web/Controllers/UpcomingController.cs

@@ -46,7 +46,7 @@ namespace NzbDrone.Web.Controllers
                 Overview = u.Overview,
                 AirDateTime = GetDateTime(u.AirDate.Value, u.Series.AirTimes),
                 AirDate = u.AirDate.Value.ToBestDateString(),
-                AirTime = String.IsNullOrEmpty(u.Series.AirTimes) ? "?" : Convert.ToDateTime(u.Series.AirTimes).ToShortTimeString(),
+                AirTime = String.IsNullOrEmpty(u.Series.AirTimes) ? "?" : Convert.ToDateTime(u.Series.AirTimes).ToString("MM/dd/yyyy"),
                 Status = u.Status.ToString()
             }).OrderBy(e => e.AirDateTime).ToList();
         }

NzbDrone.Web/Models/HistoryModel.cs

@@ -14,6 +14,7 @@ namespace NzbDrone.Web.Models
         public string NzbTitle { get; set; }
         public string Quality { get; set; }
         public string Date { get; set; }
+        public string DateSorter { get; set; }
         public bool IsProper { get; set; }
         public string Indexer { get; set; }
         public int EpisodeId { get; set; }

NzbDrone.Web/Views/History/Index.cshtml

@@ -73,6 +73,15 @@
                                 { sWidth: 'auto', "mDataProp": "EpisodeTitle", "bSortable": false }, //Episode Title
                                 { sWidth: '70px', "mDataProp": "Quality", "bSortable": false }, //Quality
                                 { sWidth: '150px', "mDataProp": "Date" }, //Grabbed On
+                                { sWidth: '150px', "mDataProp": function (source, type, val) {
+                                        // 'display' and 'filter' use our fancy naming
+                                        if (type === 'display' || type === 'filter') {
+                                            return source["Date"];
+                                        }
+                                        // 'sort' and 'type' both just use the raw data
+                                        return source["DateSorter"];
+                                    }
+                                }, //Date
                                 { sWidth: '40px', "mDataProp": "HistoryId", "bSortable": false, "fnRender": function (row) {
                                     var deleteImage = "<img src=\"../../Content/Images/X.png\" alt=\"Delete\" title=\"Delete from History\" class=\"gridImage\" onclick=\"deleteHistory(this.parentNode.parentNode, " + row.aData["HistoryId"] + ")\">";
                                     var redownloadImage = "<img src=\"../../Content/Images/Downloading.png\" alt=\"Redownload\" title=\Redownload Episode\" class=\"gridImage\" onclick=\"redownloadHistory(this.parentNode.parentNode, " + row.aData["HistoryId"] + ", " + row.aData["EpisodeId"] + ")\">";