diff --git a/application/controllers/Api.php b/application/controllers/Api.php
index 01cfccedf..418149602 100644
--- a/application/controllers/Api.php
+++ b/application/controllers/Api.php
@@ -728,6 +728,74 @@ class API extends CI_Controller {
 
 	}
 
+	// API function to check if a grid is in the logbook already
+	function logbook_get_worked_grids() {
+		$arr = array();
+		header('Content-type: application/json');
+		$this->load->model('api_model');
+		$obj = json_decode(file_get_contents("php://input"), true);
+		if ($obj === NULL) {
+		    echo json_encode(['status' => 'failed', 'reason' => "wrong JSON"]);
+		    die();
+		}
+		// Check rate limit
+		$identifier = isset($obj['key']) ? $obj['key'] : null;
+		$this->check_rate_limit('logbook_get_worked_grids', $identifier);
+
+		if(!isset($obj['key']) || $this->api_model->authorize($obj['key']) == 0) {
+		   http_response_code(401);
+		   echo json_encode(['status' => 'failed', 'reason' => "missing api key"]);
+		   die();
+		}
+		if(!isset($obj['logbook_public_slug'])) {
+		   http_response_code(400);
+		   echo json_encode(['status' => 'failed', 'reason' => "missing fields"]);
+			return;
+		}
+		if($obj['logbook_public_slug'] != "") {
+			$logbook_slug = $obj['logbook_public_slug'];
+			if(isset($obj['band'])) {
+				$band = $obj['band'];
+			} else {
+				$band = null;
+			}
+			if(isset($obj['cnfm'])) {
+				$cnfm = $obj['cnfm'];
+			} else {
+				$cnfm = null;
+			}
+			$this->load->model('logbooks_model');
+			if($this->logbooks_model->public_slug_exists($logbook_slug)) {
+				$logbook_id = $this->logbooks_model->public_slug_exists_logbook_id($logbook_slug);
+				if($logbook_id != false)
+				{
+					$logbooks_locations_array = $this->logbooks_model->list_logbook_relationships($logbook_id);
+					if (!$logbooks_locations_array) {
+						http_response_code(404);
+						echo json_encode(['status' => 'failed', 'reason' => "Empty Logbook"]);
+						die();
+					}
+				} else {
+					http_response_code(404);
+					echo json_encode(['status' => 'failed', 'reason' => $logbook_slug." has no associated station locations"]);
+					die();
+				}
+				$this->load->model('logbook_model');
+
+				$arr = $this->api_model->get_grids_worked_in_logbook($logbooks_locations_array, $band, $cnfm);
+				http_response_code(201);
+				echo json_encode($arr);
+
+			} else {
+				http_response_code(404);
+				echo json_encode(['status' => 'failed', 'reason' => "logbook not found"]);
+				die();
+			}
+
+		}
+
+	}
+
 	/* ENDPOINT for Rig Control */
 
 	function radio() {
diff --git a/application/models/Api_model.php b/application/models/Api_model.php
index b97d4753c..eda1493dc 100644
--- a/application/models/Api_model.php
+++ b/application/models/Api_model.php
@@ -178,5 +178,68 @@ class API_Model extends CI_Model {
 		";
 
 		return $this->db->query($sql, $binding);
+
+	}
+
+	function get_grids_worked_in_logbook($StationLocationsArray = null, $band = null, $cnfm = null) {
+		$grid_array = [];
+		if ($StationLocationsArray == null) {
+			$this->load->model('logbooks_model');
+			$logbooks_locations_array = $this->logbooks_model->list_logbook_relationships($this->session->userdata('active_station_logbook'));
+		} else {
+			$logbooks_locations_array = $StationLocationsArray;
+		}
+
+		$bindings = [];
+		$subsql = '';
+		$band = ($band == 'All') ? null : $band;
+		if ($band != null && $band != 'SAT') {
+			$subsql .= ' AND COL_BAND = ? AND COL_PROP_MODE != "SAT"';
+			$bindings[] = $band;
+		} else if ($band == 'SAT') {
+			$subsql .= ' AND COL_SAT_NAME != ""';
+		}
+		switch ($cnfm) {
+			case 'qsl':
+				$subsql .= ' AND COL_QSL_RCVD = "Y"';
+				break;
+			case 'lotw':
+				$subsql .= ' AND COL_LOTW_QSL_RCVD = "Y"';
+				break;
+			case 'eqsl':
+				$subsql .= ' AND COL_EQSL_QSL_RCVD = "Y"';
+				break;
+		}
+
+		$ids = array_map('intval', $logbooks_locations_array);
+		$sql = 'SELECT DISTINCT UPPER(SUBSTR(COL_GRIDSQUARE, 1, 4)) AS gridsquare FROM ' . $this->config->item('table_name') . ' thcv ';
+		$sql .= ' WHERE COL_GRIDSQUARE <> "" AND CHAR_LENGTH(COL_GRIDSQUARE) >= 4';
+		$sql .= ' AND station_id IN (' . implode(',', $ids) . ')';
+		$sql .= $subsql;
+		$sql .= ' ORDER BY gridsquare ASC;';
+		$query = $this->db->query($sql,$bindings);
+		foreach($query->result() as $line) {
+			$grid_array[] = $line->gridsquare;
+		}
+		// Get and add VUCC grids
+		$sql = 'SELECT DISTINCT UPPER(COL_VUCC_GRIDS) AS vuccgrids FROM ' . $this->config->item('table_name') . ' thcv ';
+		$sql .= ' WHERE COL_VUCC_GRIDS <> ""';
+		$sql .= ' AND station_id IN (' . implode(',', $ids) . ')';
+		$sql .= $subsql;
+		$sql .= ' ORDER BY vuccgrids ASC;';
+		$query = $this->db->query($sql,$bindings);
+		foreach($query->result() as $line) {
+			$vucc_grids = explode(',', $line->vuccgrids);
+			foreach ($vucc_grids as $vucc_grid) {
+				if (strlen($vucc_grid) >= 4) {
+					$grid = substr($vucc_grid, 0, 4);
+					if (! in_array($grid, $grid_array)) {
+						$grid_array[] = $grid;
+					}
+				}
+			}
+		}
+		sort ($grid_array);
+		return $grid_array;
 	}
 }